Do not add current tenant to private flavor access

Avoid adding the current tenant to the flavor access list when
a private flavor is created. In ordeir to add tenants to the
flavor access list we should use the add_tenant api.

Tempest has to be updated accordingly:
https://review.openstack.org/81551

Documentation has to be updated as well:
https://review.openstack.org/82175

Partially (just for the V2 API rather than V2 and V3)
reverts commit 6ba248635b70860a44e486e7739efa4cc6612ce6

Fixes unittest which was added in the original commit so it checks
for the behaviour we have now rather than the behaviour after the
backwards incompatible change which is being reverted.

Change-Id: I731081b6df0d96df1bc1763d214d28c62bbbb51c
Closes-Bug: #1286297
Merge "Do not add current tenant to private flavor access"