Update Gemfile to use the new omnibus-ruby branch

With a major refactoring of the omnibus-openstack code, I was able to
minimize my changes to omnibus-ruby. Therefore, update the Gemfile here
accordingly.
Update Vagrantfile to use yaml config

YAML is a much more readable format than json. Both can be parsed by
the YAML parser, so both are viable options. However, YAML allows me to
add much-needed comments.
Remove json example in favor of yaml example

yaml is more human-friendly than json, though both will work. Moving
this example to use yaml only at this point. Will backfill with
documentation indicating that both can be used.
version attributes were in the wrong place

version attributes are part of the top-level omnibus namespace, not
a part of source...counter-intuitive as that may be.
Update Gemfile.lock to bring omnibus-ruby changes

I made some changes to my fork of omnibus-ruby. So, update the Gemfile
accordingly.