Merge the following from ^/projects/release-vmimage:
r273076, r273077, r273079, r273095:

r273076:
  Add a separate make(1) target to release/Makefile to
  build FreeBSD virtual machine disk images for use on
  the Microsoft Azure service.

  For now, this target is not directly connected to the
  build, however can be manually invoked.

  The 'vm-azure' target invokes {amd64,i386}/mk-azure.sh,
  which does the heavy lifting to produce proper VHDs.
  mk-azure.sh uses a configuration file, defaulting to
  tools/azure.conf if otherwise unset.

r273077:
  Clear VM_RC_LIST.

r273079:
  Fix signal list to trigger umount(8).

r273095:
  Output an informational message when mkimg(1) runs, so it
  does not appear that the process has stopped while waiting
  for a 'y/n' response when waagent is deprovisioned.

Tested on:	releng/10.1@r272876
MFC after:	3 days
X-MFC-10.1:	yes
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273096 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f