Occasional chroot problem caused by pylxd not found

[Adam Collard]

https://launchpadlibrarian.net/465354782/buildlog_snap_ubuntu_bionic_amd64_maas-2.7_BUILDING.txt.gz

From my naive reading of the traceback, when attempting to load an image into LXD, lpbuildd can fail.

Traceback (most recent call last):
  File "/usr/share/launchpad-buildd/bin/in-target", line 27, in <module>
    sys.exit(main())
  File "/usr/share/launchpad-buildd/bin/in-target", line 23, in main
    return args.operation.run()
  File "/usr/lib/python2.7/dist-packages/lpbuildd/target/lifecycle.py", line 32, in run
    self.backend.create(self.args.image_path, self.args.image_type)
  File "/usr/lib/python2.7/dist-packages/lpbuildd/target/lxd.py", line 218, in create
    image = self.client.images.create(image_file.read(), wait=True)
  File "/usr/lib/python2.7/dist-packages/pylxd/image.py", line 94, in create
    Operation.wait_for_operation(client, response.json()['operation'])
  File "/usr/lib/python2.7/dist-packages/pylxd/operation.py", line 31, in wait_for_operation
    operation = cls.get(client, operation_id)
  File "/usr/lib/python2.7/dist-packages/pylxd/operation.py", line 40, in get
    response = client.api.operations[operation_id].get()
  File "/usr/lib/python2.7/dist-packages/pylxd/client.py", line 86, in get
    self._assert_response(response)
  File "/usr/lib/python2.7/dist-packages/pylxd/client.py", line 66, in _assert_response
    raise exceptions.LXDAPIException(response)
pylxd.exceptions.LXDAPIException: not found

This caused the build to hang for many minutes before being marked as a chroot failure.