Move virtual machine / cloud provider targets and
options from release/Makefile to their own Makefile.

Sponsored by:	The FreeBSD Foundation
Add glue to allow enabling building cloud provider
VM images by default.

When WITH_CLOUDWARE is not empty, add CLOUDTARGETS
to the release/Makefile 'release' target.

CLOUDTARGETS is generated from the contents of
CLOUDWARE, which should be a list of all supported
target providers.

Sponsored by:	The FreeBSD Foundation
Avoid hard-coding the Azure image file format.
While here, avoid using OSRELEASE for the output
file name.

Sponsored by:	The FreeBSD Foundation
Remove a few vestiges of passing an exit code to
panic().

Sponsored by:	The FreeBSD Foundation
Initial commit providing a mechanism to create
openstack images as part of the release build.

This mimics the way Microsoft Azure images are
built, with the addition of installing the
net/cloud-init package and adding a (commented)
rc.conf(5) entry for cloudinit.

Sponsored by:	The FreeBSD Foundation
Fix output file name for openstack images.
No further conversion is necessary for this
VM file target, so there is no need to append
the '.raw' suffix here.

Sponsored by:	The FreeBSD Foundation
Uncomment the cloudinit rc.conf(5) line.

Sponsored by:	The FreeBSD Foundation