Reduce RAM overprovision ratio.

A ratio of 1.3 will still allow a few new instances to be
created.  Our whole cluster is already over 1.2 :(

(Note that a previous version of this patch used incorrect
syntax for the variable, due to following docs for the wrong
OpenStack version)

Change-Id: I638cb6c2573f161d28c69fc7c5f765c4a5a45d7f
Merge "Reduce RAM overprovision ratio." into production