Fix init of test_volume_type_extra_specs_list

* test_volume_type_extra_specs_list relied on another test running
  first to create a volume type extra spec. When the tests are run
  in parallel (or if the test is run by itself), the test can fail
  if a suitable test to perform the initialisation is not run
  before it does. This patch adds the required volume type extra spec
  creation to the test

* test_volume_type_extra_specs_update relied on another test running
  before it to create a volume type extra spec which it would update.
  Now create it within the test itself

* Create unique extra_specs for each test. This should reduce the probability
  of changes in the future resulting in tests accidentally relying on each other

* Combines *_create_delete and *_create_get tests into one _create_get_delete test

Change-Id: Ieffc20599d98ee33d1d2ac41ec0abe812a1afab5
Merge "Fix init of test_volume_type_extra_specs_list"