Switch to using bundletester for execution of functional tests,
leveraging tox to build out test virtualenvs.
Rename amulet tests inline with gate-*, dev-* and dfs-*
naming standards.
Update README to refer to functional testing section of the charm
guide.
Also remove brittle auth conf checks which are failing at
cinder-ceph master. Even without those explicit checks, if auth
fails, functional tests will still fail and catch issues in gate.
Change-Id: I7b0009fa0e29dcaf7d6e5607af7b397e437aac79