Prevent us from sleeping during DB retry tests
Prevent us from sleeping during DB retry tests

Unit tests should never *actually* sleep. Some of the DB API tests
that poke the retry wrapper in oslo.db trigger situations that would
call time.sleep(). This is part of a desirable exponential backoff
timer in oslo.db, but there's no reason to actually wait to call
the next mock in a unit test. So, mock out sleep for those tests.
Before this, the single-thread time to run test_db_api was 289s,
and afterwards it is 133s.

Change-Id: I0492b497000585f079691ae863b2b2ebf078795d

Juniper/nova,klmitch/nova,phenoxim/nova,cloudbase/nova,mikalstill/nova,rajalokan/nova,jianghuaw/nova,openstack/nova,gooddata/openstack-nova,alaski/nova,sebrandon1/nova,phenoxim/nova,hanlind/nova,jianghuaw/nova,Juniper/nova,rahulunair/nova,Juniper/nova,mikalstill/nova,openstack/nova,mahak/nova,rahulunair/nova,klmitch/nova,cloudbase/nova,sebrandon1/nova,vmturbo/nova,mahak/nova,vmturbo/nova,alaski/nova,gooddata/openstack-nova,rajalokan/nova,jianghuaw/nova,rajalokan/nova,vmturbo/nova,gooddata/openstack-nova,openstack/nova,sebrandon1/nova,rajalokan/nova,klmitch/nova,mahak/nova,jianghuaw/nova,hanlind/nova,Juniper/nova,rahulunair/nova,gooddata/openstack-nova,klmitch/nova,vmturbo/nova,mikalstill/nova,cloudbase/nova,hanlind/nova