Credentials should be specified in the accounts file
as described in the Tempest configuration guide
(http://docs.openstack.org/developer/tempest/configuration.html).
Specifying credentials in the identity section of the tempest
config file is deprecated.
If the user provides credentials in the identity section of tempest
config file and does not provide accounts file, show a warning
that this is deprecated and will be not supported in the future.
If the user does not provide credentials at all, show an error and
exit.
Show information to the user how to configure the credentials.
Update the refstack-client unit tests that still use the identity
section to use accounts file instead.
Change-Id: I6eab3b587292a35404c93da35914ad1f53ef49c7
Closes-Bug: #1552377
b066bd68a8