Only run relevant puppet apply tests

Associate an OS with each node defined in site.pp so that the puppet
apply test will only test nodes apprapriate to the node the test
is running on.

Fix remaining errors related to this test, and make it vote.

Also, start running the centos6 version regularly
(which is still non-voting).

Change-Id: I26722dce15589c982af5de36f8ccf42666d29f2b
Merge "Only run relevant puppet apply tests"