Snapcraft tutorial errors out on OSX with multipass error, "returned exit code 2"

[Daniel O'Brien]

Attempting to run through the Go tutorial on OSX results in the following when running `snapcraft` the first time:

```
Launching a VM.
Launched: snapcraft-test-httplab-dobs
2019-12-16T15:57:59Z INFO Waiting for restart...
snapd 2.42.5 from Canonical✓ installed
core18 20191126 from Canonical✓ installed
snapcraft 3.8 from Canonical✓ installed
Ign:1 http://security.ubuntu.com/ubuntu bionic-security InRelease
Ign:2 http://archive.ubuntu.com/ubuntu bionic InRelease
Ign:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Err:4 http://security.ubuntu.com/ubuntu bionic-security Release
  404 Not Found [IP: 91.189.91.14 80]
Ign:5 http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Err:6 http://archive.ubuntu.com/ubuntu bionic Release
  404 Not Found [IP: 91.189.88.24 80]
Err:7 http://archive.ubuntu.com/ubuntu bionic-updates Release
  404 Not Found [IP: 91.189.88.24 80]
Err:8 http://archive.ubuntu.com/ubuntu bionic-backports Release
  404 Not Found [IP: 91.189.88.24 80]
Reading package lists... Done
E: The repository 'http://security.ubuntu.com/ubuntu bionic-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu bionic-updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu bionic-backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
Failed to update the package cache: Some files could not be downloaded:

failed to run apt update

Check that the sources on your host are configured correctly.
An error occurred when trying to execute 'sudo -i env SNAPCRAFT_HAS_TTY=True snapcraft refresh' with 'multipass': returned exit code 2.
```

On subsequent runs:

```
Launching a VM.
snap "snapd" has no updates available
snap "core18" has no updates available
snap "snapcraft" has no updates available
mount failed: Error enabling mount support in 'snapcraft-test-httplab-dobs'
An error occurred with the instance when trying to mount with 'multipass': returned exit code 2.
Ensure that 'multipass' is setup correctly and try again.
```

I've confirmed that multipass is running, though unclear how to confirm that it's set up "correctly."

Based on others' incidents I attempted to run `snapcraft clean`, the result was the following:

```
Sorry, an error occurred in Snapcraft:
module 'os' has no attribute 'sched_getaffinity'
Traceback (most recent call last):
  File "/usr/local/bin/snapcraft", line 8, in <module>
    sys.exit(run())
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/cli/_command.py", line 87, in invoke
    return super().invoke(ctx)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/cli/lifecycle.py", line 338, in clean
    lifecycle.clean(project, parts, steps.PRIME)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/internal/lifecycle/_clean.py", line 198, in clean
    config = project_loader.load_config(project)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/internal/project_loader/__init__.py", line 47, in load_config
    return Config(project)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/internal/project_loader/_config.py", line 212, in __init__
    self.data = self._expand_env(snapcraft_yaml)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/internal/project_loader/_config.py", line 335, in _expand_env
    snapcraft_global_environment(self.project)
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/internal/project_loader/_env.py", line 110, in snapcraft_global_environment
    "SNAPCRAFT_PARALLEL_BUILD_COUNT": str(project.parallel_build_count),
  File "/usr/local/Cellar/snapcraft/3.9/libexec/lib/python3.7/site-packages/snapcraft/project/_project_options.py", line 135, in parallel_build_count
    return len(os.sched_getaffinity(0))
AttributeError: module 'os' has no attribute 'sched_getaffinity'
We would appreciate it if you created a bug report at
https://launchpad.net/snapcraft/+filebug with the above text included.
You can find the traceback in file '/var/folders/8t/bcy9yfg90c56_4m_36wmtyrm0000gp/T/tmp4o1p110g/trace.txt'.
```

Which led me here.

[Sergio Schvezov (sergiusens)]

It seems that networking is not fully up.

We will work on the snapcraft side to better expose this and cleanup if bootstrapping fails.