Add 'cloudware-install' target to handle copying cloud
disk images to a directory within DESTDIR.

Add CLOUDINSTALL variable to automatically generate the
actual list of install targets.  While here, rename the
cloud-specific names from 'vm-' to 'cw-' to avoid naming
collisions.

Add AZURE_DISK, GCE_DISK, and OPENSTACK_DISK output file
variables.

Add 'cloudware-install' to the 'install' target.

Remove a stale comment.

Add a CLOUDPACKAGE variable to contain a list of targets for
post-install packaging cloud provider images.

Add a 'gce-package.sh' script to generate the final output
image ready for upload to the GCE platform.  Right now, this
is the only image that has a specific output format (GNU-tar),
and this implementation is expected to be temporary.

This is not directly connected to the other release targets.