On OVH and Bluebox, the memory layout is such that there is still
significant (~900M) memory above the 8192M address. Increase the
limit to encompass that, which will bring these providers up to
approximately 8G, while increasing hpcloud (which is the actual
target of this restriction) to about 8.5G.
Change-Id: I5c121be55cadad13ad5807968f33b492f9b1e215