Add compute notifications tests for ceilometer

Added ceilometer test for measurements:
instance, instance:<type>, memory, vcpus, disk.root.size,
disk.ephemeral.size

Change-Id: Ic99229d38f17cd81e147d86031aca75c13171057
Partially implements: blueprint add-basic-ceilometer-tests
Merge "Add compute notifications tests for ceilometer"
Merge branch 'master' of https://github.com/openstack/tempest