MFC r313021, r313027, r313044:

r313021 (brd):
Force a few variables to be upper case when they are evaulated.

r313027 (brd):
Add a new vagrant-box target, to make it easier and less redundant
to only produce the Vagrant box and not upload it.

r313044 (brd):
Add some comments with examples on how to build Vagrant images.

Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Remove '-' separating OSRELEASE and SNAPSHOT_DATE for vagrant
builds, and prepend it to SNAPSHOT_DATE to prevent a trailing '-'
in the final box name for a release build.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Add support for building VirtualBox Vagrant images.
Abstract the build, package and upload to handle building either type.

Approved by: re (gjb)

Remove the HH-MM suffix from the build date suffix.

It was useful when working out several kinks when
testing automated image uploading when retrying was
necessary, but now it is making things much too messy.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Default the VAGRANT_VERSION to ${REVISION}-${BRANCH} if
not set, which expands to '11.0-CURRENT', for example.

If the branch is -CURRENT, -STABLE, or -PRERELEASE, suffix
the VAGRANT_VERSION with the snapshot date.

MFC after: 3 days
X-MFC-Needs: r284893, r284895, r284896, r284897, r284942
Tested with: head@r284961 (patched)
Sponsored by: The FreeBSD Foundation

Add Support for uploading Vagrant images to Hashicorp Atlas.

Approved by: re (gjb)

Instead of hard-coding the PROVIDERS for upload, add the
VAGRANT_PROVIDERS variable. Right now, it defaults to only
vmware_desktop, virtualbox support is to follow at some point.

While here, fix the hashicorp URL: s/vagrant/atlas/, which
was result of a sed(1) replace (and my fault).

Sponsored by: The FreeBSD Foundation

Remove _ACCOUNT and add _USERNAME, _NAME, _VERSION for the
VAGRANT_${VAR} variables extracted from VAGRANT_UPLOAD_CONF.

Set ATLAS_${VAR} to VAGRANT_${VAR} if VAGRANT_UPLOAD_CONF
is set. There is intent to intentionally have separate
variants of configuration entries, but the defaults do not
yet have any reason to be different.

Sponsored by: The FreeBSD Foundation

Add default VAGRANT_IMG variable.

Sponsored by: The FreeBSD Foundation

Add initial support for building Vagrant images for VMWare. Next steps will be adding Virtualbox support and uploading to Hashicorp Atlas for others to consume.

Approved by: re (gjb)