unused abstract class definitions in storage driver tests

[Terri Yu]

DBTestBase and EventTestBase are defined as abstract classes in tests/storage/base.py

However, neither of these classes has defined any abstract methods, so the abstract class definitions are unnecessary.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/41000

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/41000
Committed: http://github.com/openstack/ceilometer/commit/51cd25c6b241b308d5cf840c1221f8f0d5b2ce54
Submitter: Jenkins
Branch: master

commit 51cd25c6b241b308d5cf840c1221f8f0d5b2ce54
Author: Terri Yu <email address hidden>
Date: Fri Aug 9 01:00:20 2013 +0000

    Remove unused abstract class definitions

    Fixes bug #1210281

    Removed abstract classes definitions from DBTestBase and EventTestBase classes
    in storage driver tests since they are not used. Neither of these classes has
    defined any abstract methods, so the abstract class definitions are unnecessary.

    Also removed import statement for abstract base classes since there are now no
    abstract class definitions.

    Change-Id: I0b5b487631d780ba2ab087dce2ef340f126f8a69