Fix OSTFs with Ceilometer

[Andrey Setyaev]

Description:
We don't have TestVM image due to disabled 'nova' AZ. So we wish to see these tests with TestVM-VMDK image only.

Actual behaviour:
AssertionError: Failed 3 OSTF tests; should fail 0 tests. Names of failed tests:
  - Ceilometer test to check alarm state and get Nova notifications (failure) TestVM image not found. Please, download http://download.cirros-cloud.net/0.3.1/cirros-0.3.1-x86_64-disk.img image and register it in Glance with name 'TestVM' as 'admin' tenant.
  - Ceilometer test to check events and traits (failure) TestVM image not found. Please, download http://download.cirros-cloud.net/0.3.1/cirros-0.3.1-x86_64-disk.img image and register it in Glance with name 'TestVM' as 'admin' tenant.
  - Ceilometer test to create, check and list samples (failure) TestVM image not found. Please, download http://download.cirros-cloud.net/0.3.1/cirros-0.3.1-x86_64-disk.img image and register it in Glance with name 'TestVM' as 'admin' tenant.

Expected behaviour:
Tests passed.