Disable the v2.0 identity API by default

The v2.0 identity API is being removed in the Queens release, but in
order to do so we need to stop some v2.0 tempests tests from being
run. This commit switches the default to disable the keystone v2 api.
In a future commit after the removal of the api from keystone the bits
to deploy the v2 api will be removed.

Change-Id: I5afcba6321f496b8170be27789bee7c9ad8eacce
1 file changed