Increased RAM size for master node VM to 1.5Gb

With introduction of Docker, master node requirements
are increased and 1Gb of RAM doesn't seem to be enough:
Linux starts to use swap. To avoid this and speed up
master node boostrapping, increasing default RAM size.

Change-Id: Ib6ed191b49729f480388b0414c8407571242ce84
Related-Bug: 1319678