Tempest tests for glance import workflow

This adds an initial test for glance image interoperable import
that uses the glance-direct method. It will skip if the server
does not support glance-direct.

Adding feature flag to enable the import tests as devstack on
stable branches cannot support image import feature.

Change-Id: I09e7fb4e7758edd5256ae70ceeea6f143466c3e3
6 files changed