Power architectures (arch.PPC64LE and arch.PPC64) support huge pages and
transparent huge pages. This patch just enables it on nova libvirt driver. A
reno note was also added to track this new feature.
This change also enables the test_does_want_hugepages unit test to run on the
architectures that support huge pages.
Closes-bug: #1617081
Change-Id: I22bc57a0b244667c716a54ca37c175f26a87a1e9