* devel-2.5:
  Allow per-hypervisor optional files
  Add hypervisors ancillary files list
  xen: abstract a few hardcoded strings as constants

Conflicts:
	lib/cmdlib.py
	  - trivial

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>