status: New builtin for system administrators to see deployments

This allows administrators to configure between deployments and easily see which deployment
they are booted into as well as indicating which is chronologically most recent.  This makes
the process more user-friendly, rather than requiring the user to remember which deployment
checksum corresponds to the most recent upgrade.
Merge branch 'master' of http://github.com/aloverso/rpm-ostree

* 'master' of http://github.com/aloverso/rpm-ostree:
  status: New builtin for system administrators to see deployments
 Add "rpm" command, for doing rpm/yum queries on commits.

 It currently has the following sub-commands:

diff COMMIT COMMIT
 for rpmtree diff.
list [prefix...] COMMIT...
 for "yum list" like command.
version COMMIT...
 for "yum version" like command.

...bunch of FIXME's, UI output isn't great, needs docs.
 We also don't use the same code as the treediff on upgrade atm.