Adding baremetal guard to RamWeigher

-negative RAM weight should be only for
 undercloud (baremetal)
-this is quick fix, patch that is making it
 configurable via heat is coming

Change-Id: I96bf33eae7fa1e36c788bab957cf88e291f50fa0
Fixes-bug: #1300458
Merge "Adding baremetal guard to RamWeigher"