Tempest tests were not appropriate for driver-assisted migration,
so this was fixed.
Also, improved docstrings and fixed workflow for drivers when
implementing 2-phase migration to be accurate with tempest and
handle AZs, which were previously locked to the source share's
AZ.
Driver-assisted migration now creates an additional
share instance to better handle and support driver methods.
Updated allow_access and deny_access APIs to allow users to mount
migrating shares before issuing 'migration-complete'.
APIImpact
Closes-bug: #1594922
Change-Id: If4bfaf7e9d963b83c13a6fea241c2eda14f7f409
c7fe51e79b