Role vars have a higher precedence than role defaults. This allows to
import default vars from another role via vars_files without overriding
project_name (see closed bug for details).
Compared to victoria, this cherry picked change includes the congress,
mongodb and nova-hyperv roles.
Change-Id: I3d919736e53d6f3e1a70d1267cf42c8d2c0ad221
Closes-Bug: #1951785
(cherry picked from commit 56fc74f231)
(cherry picked from commit 6c695564bc)
(cherry picked from commit 6cb0e10626)
(cherry picked from commit 145e64d5ca)
229c3ad585