Replace tests.base part6

It is the sixth step to replace using ceilometer.tests.base with
openstack.common.test.
In this patch is changed for using
openstack.common.test and added needed fixtures in
test classes.
Added in ceilometer.tests.db code from ceilomete.tests.base
because ceilometer.tests.base will not be used in the future.

Change-Id: I3cacca4eff19eae8874decd892ab1225f95cfee9
Merge "Replace tests.base part6"