Update devstack-cache.py to install RPMs.

Change-Id: I952c0b474218552a98ad3f499fc0e7f3eba67e23
Add merge-release-tags job to Savanna

Change-Id: I66d8683f4b1f68ddb38d1b0c95b43c28985b18a3
Merge "Add merge-release-tags job to Savanna"
Merge "Update devstack-cache.py to install RPMs."