Code dedup in class QuotaReserveSqlAlchemyTestCase

Moved common parts to setUp()
   -quotas
   -deltas
   -usages
Move reservations update and usages init to separate functions

bp nova-tests-code-duplication

Change-Id: I03efed0d1f40ba7670c919efed4fdafaf59576f8
Merge "Code dedup in class QuotaReserveSqlAlchemyTestCase"