Unhardcoding stores parameter in glance_store section

The patch changes the logic which was the following if server.storage.engine
has file engine then stores is defined as file,http therefore due to
this there was a chance to use "file" engine with any extra engines like
rdb, swift etc.

Change-Id: I32c71487edec4601bea4374413befe78495c1601
Related-PROD: PROD-26281 (PROD:26281)
(cherry picked from commit f5a826eb275f3cbc1ae20858be0716fc5c4cf98d)
3 files changed