systemd services created by snappy breaks etckeeper

[Jay R. Wren]

etckeeper uses bzr to version files in etc to allow for rollback on configuration changes.

The '\x2d' character prevents bzr from versioning this file and displays a very ugly error.

/etc/systemd/system/snap-ubuntu\x2dcore-122.mount

bzr: ERROR: bzrlib.errors.InvalidEntryName: Invalid entry name: snap-ubuntu\x2dcore-122.mount

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/builtins.py", line 842, in run
    no_recurse, action=action, save=not dry_run)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 52, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 453, in smart_add
    adder.add(file_list, recurse=recurse)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 764, in add
    inv_path)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 628, in _add_one_and_parent
    file_id=file_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 2234, in make_entry
    return factory(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 422, in __init__
    super(InventoryFile, self).__init__(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 222, in __init__
    raise errors.InvalidEntryName(name=name)
InvalidEntryName: Invalid entry name: snap-ubuntu\x2dcore-122.mount

bzr 2.7.0 on python 2.7.11 (Linux-4.4.0-24-generic-x86_64-with-
    Ubuntu-16.04-xenial)
arguments: ['/usr/bin/bzr', 'add', '-q', '.']
plugins: bash_completion[2.7.0], builddeb[2.8.6], builder[0.7.3],
    bzrtools[2.6.0], changelog_merge[2.7.0], etckeeper[unknown], git[0.6.12],
    grep[2.7.0], launchpad[2.7.0], loggerhead[1.18.1],
    netrc_credential_store[2.7.0], news_merge[2.7.0], po_merge[2.7.0],
    search[1.7.0dev], weave_fmt[2.7.0]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.
etckeeper warning: bzr add failed

[Jay R. Wren (evarlast)]

A fix might be to write to /etc/.bzrignore or /etc/.gitignore if it exists

    systemd/system/snap-ubuntu*

[Jamie Strandboge (jdstrand)]

The bzr bug in question is bug #1035045. Since it seems the bug won't be fixed in bzr, it might be useful as Jay mentioned to adjust etckeeper to ignore these files.

[Gustavo Niemeyer (niemeyer)]

This is a bug in etckeeper. The "\x2d" character is inserted by systemd's escape routine itself:

    $ systemd-escape foo-bar
    foo\x2dbar

We'll likely stop using the escaping logic and use simpler names now that we're constraining application names further, but somebody else using systemd-escape will hit the same bug.

[JP Vossen (jp-jpsdomain)]

The hack-around in https://bugs.launchpad.net/ubuntu/+source/bzr/+bug/1035045/comments/3 "worked" for me with `etckeeper` + BZR on Mint-18, in that it stopped the error messages. I don't actually know or care what omitting the affected snap files in `/etc/` might do later.

Note I needed 2 lines in `/etc/.bzrignore` and was confused when the first line failed to work. And you probably also need to:
```
# Be root
cd /etc
sudo vi .bzrignore
 systemd/system/snap*
 systemd/system/multi-user.target.wants/snap*
bzr rm --keep systemd/system/snap* systemd/system/multi-user.target.wants/snap*
etckeeper commit 'Ugly hack-around for bzr/etckeeper errors for snapd use of backslash in file names'
```