Add HPCloud region-a to nodepool.

Use the second new region available to us in HPCloud. Region-b appears
to be working well, add region-a to the mix as part of the move away
from using resources on the old hpcloud AZs.

Change-Id: I809303c5dd2f25f2b4dad638568fe4b8b1059818
Merge "Add HPCloud region-a to nodepool."