In order to expose the var in role documentation and to allow the use
of dynamically set facts to override the value in CI environments the
variables are moved from the role vars to the role defaults.
The test preparation implements an override of the URL for OpenStack-CI
to make use of the local mirrors.
The variable to enable/disable the use of UCA has been standardised
to the same as the os_nova role.
Change-Id: I442f6dca8345f78848536f2fc923b72be8a6d092
1240dd0cf0