This change draws on the charms.openstack and layer-openstack-api
changes to provide the ability to configure the number of workers that
the manila charm starts for API usage.
* Packages the manila charm into a venv. This is because the
subordinate charms are ALSO reactive, which means that different
versions of either charms.reactive or charms.openstack could be
overwritten from the subordinate charm.
* Band-aid an issue with manila-share not being started even though all
of the config is properly set. This uses the update-status hook to
check to see if the manila-share service should be running.
* Work-around for a bug in python-manilaclient (Bug: #1707303) which
caused basic_deployment test 400 to fail.