Add ceilometer keystone notifications tests to ostf

Added ceilometer tests for keystone notifications:
identity.user.created, identity.user.deleted, identity.user.updated
identity.role.created, identity.role.updated, identity.role.deleted
identity.project.created, identity.project.updated, identity.project.deleted
identity.group.created, identity.group.updated, identity.group.deleted
identity.trust.created, identity.trust.deleted

Changed actual duration for ceilometer tests in relation to recent
changes in ceilometer

Partially implements: blueprint ceilometer-ostf-notification-tests

Change-Id: I4f488166223ca6bbd294815e6bff7215ad6009ba
Merge "Add ceilometer keystone notifications tests to ostf"