Adds keystone roles v2 tests in v3

This submission is to add the tests missing in v3 and present in v2.
Submitting roles test cases.

Change-Id: I0e995848ed0019a4895cdff2b70795b5eaf9795a
Add network service tag to compute tests

This commit adds the network service tag to all the compute api tests
that are using network services so that they're properly tagged.

Partially implements bp add-service-tags

Change-Id: I0b3436e4b3a2f1c2285a17718ecb8e413bc60269
Sahara: minor changes for API tests

In file "test_cluster_templates.py" setUpClass method needs
to be wrapped in decorator "safe_setup" because resource
(node group template) is created in setUpClass method.

In addition small code refactoring in tests for data sources was made.

Partially implements: blueprint savanna-api-tests

Change-Id: If783df527fc23ea197c5344a67e1aa3e82774b2c
Fix disk_available_least in JSON schemas

The hypervisor JSON schemas were not consistent with the value for
disk_available_least. One allowed for 'null' values, but the other
two did not. This allows 'null' in all schemas (Ironic does not
set this value so it will be 'null' when the compute api tests
are run).

Closes-Bug: #1337416

Change-Id: I71e6c5f0800f7641c49d8058596831f011328ec2
Merge "Sahara: minor changes for API tests"
Merge "Fix disk_available_least in JSON schemas"
Merge "Add network service tag to compute tests"
Merge "Adds keystone roles v2 tests in v3"
Merge branch 'master' of https://github.com/openstack/tempest