Update tox.ini to lint unit_tests, clean lint.
Add src/README.md placeholder to prevent inheritence of the
lower layer readme file in the built charm.
Add src/tox.ini and test-requirements for Amulet prep.
Update metadata.yaml for series.
Update tox.ini to minimize and clarify pep8 ignores.
Resolve flake8/pbr test-requirements version range conflict.
Mock apt in unit tests.
Add required tags data in src/metadata.yaml for charm proof.
Use openstack/charms.openstack proper in test-requirements
instead of a user space fork.
Update src/layer.yaml repo value to point to official location
and remove unnecessary options.
Change-Id: I5ca9e6cf9f8f91b3ce0ec3b48cf63535ca37c0f7