rebase: Make use of new upgrader API to ignore unconfigured state

"atomic rebase" is mostly a copy of "ostree admin switch", so let's
also pick up the changes in ostree admin switch for the new
unconfigured state flag.

This allows a user to "atomic rebase" on an unconfigured system.

Related: #31
packaging: Add symlink for atomic
Release 2014.107
status: Consistently use malloc'd() memory for status

This crashed when "atomic status" on an origin that didn't have a
refspec, which happened via my new atomic-pkglayer demo script.