Move fake_quotas and fake_get_quotas into a class

fake_quotas and fake_get_quotas are used in ExtendedQuotasTest only,
and this patch moves them into the class for cleanup.
In addition, this patch moves the mox settings into setUp() method
for the same purpose.

Change-Id: I9920d6207bb27537e6d4e738d69d59f7ed255240
Merge "Move fake_quotas and fake_get_quotas into a class"