python plugin breaks data_files in setup.py

[Blake Rouse]

Previous python3 plugin placed data_files into the snap, new plugin wants to place them in the / root of the build machine.

    copying build/lib/maas/demo.py -> /home/blake/Code/maas/maas-snap-early/parts/maas/install/lib/python3.5/site-packages/maas
    running install_data
    copying etc/maas/drivers.yaml -> /etc/maas
    error: could not create '/etc/maas/drivers.yaml': Permission denied

    ----------------------------------------
Command "/usr/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-qzcs5vfb-build/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-dz0p43th-record/install-record.txt --single-version-externally-managed --no-compile --user --prefix=" failed with error code 1 in /tmp/pip-qzcs5vfb-build/
Command '['/bin/sh', '/tmp/tmp80qny842', 'pip', 'install', '--user', '--no-compile', '--disable-pip-version-check', '--no-index', '--find-links', '/home/blake/Code/maas/maas-snap-early/parts/maas/packages', '.']' returned non-zero exit status 1

[Sergio Schvezov (sergiusens)]

https://github.com/snapcore/snapcraft/pull/861

[Leo Arias (elopio)]

Hello Blake.

Can you please share your snapcraft.yaml, so we can verify if this bug is fixed before the release?

Thanks.