cinder v2 api tests - fix volume client

This is a legacy problem in change
I712a90d39981564af09393ed1b7f4be12897c808

1. move cls.volumes_client, cls.volumes_extension_client
   cls.snapshots_client from BaseVolumeTest into
   subclass(BaseVolumeV1Test)
2. delete call cls.volumes_client.keystone_auth as it is
   called automatically in request method of RestClient.

Change-Id: I5184de9911e3fe9a3c23c2c4f84e59596f10b77c
Implements: blueprint cinder-v2-api-tests
Update README.rst with details about unit tests

This commit just fixes a couple of issues with the README file and adds
some details about the OS_TEST_PATH env variable and unit tests.

Closes-bug: #1268440

Change-Id: I17f75f7d7b3a2ac75eac884bc403bc46d6a2e77f
Fixing typo "existant". Must be "existent"

Negative tests that use the word "existant" are being corrected to "existent".
The current framework has random usage of the word 'existant' instead of
'existent'.

Change-Id: I4219c372befbd8235757f124d1414317d9b01f72
Move console output log place in test_cross_tenant_connectivity

Previous place missed to log when we fail to
verify mac address in the VM.

Change-Id: I58b68cbfdee8780fd213ec6b651c5374d5430045
Merge "Move console output log place in test_cross_tenant_connectivity"
Merge "Fixing typo "existant". Must be "existent""
Merge "cinder v2 api tests - fix volume client"
Merge "Update README.rst with details about unit tests"
Merge branch 'master' of https://github.com/openstack/tempest