Skip simple_tenant_usage related tests

This patch adds skip decorator for simple_tenant_usage related tests.
After use 'project' instead of 'tenant' in simple_tenant_usage v3,
will update those tests.

Related patches:
https://review.openstack.org/#/c/58443/
https://review.openstack.org/#/c/58444/

Change-Id: Ifcb30d1eade2b7a7196c3c0a6b4165e5fdce2944
Related-Bug: #1265416
Add coverage option to run_tests.sh

This commit adds a new option to run_tests.sh to run the unit tests
with coverage enabled. If the coverage arg is specified a coverage
report will be generated after the unit tests are run.

Change-Id: I1473fe4da96aecd0b3b0bf3a3ec1e3e87039271b
Merge "Skip simple_tenant_usage related tests"
Merge "Add coverage option to run_tests.sh"