Refactor share metadata tests to use DB
Refactor share metadata tests to use DB

For the moment tests in 'manila.tests.api.v1.test_share_metadata' module
mock all DB requests.
It leads to failures in main code if we use DB-specific things.
So, refactor all tests in that module to use test DB to unblock usage of
DB-specific things.

Change-Id: Ia584e3e6bd02f937df7630a1d09d49c888f77c8f
Partial-Bug: #1528227

vponomaryov/manila,bswartz/manila,bswartz/manila,openstack/manila,openstack/manila,NetApp/manila,vponomaryov/manila,scality/manila,scality/manila,NetApp/manila