status: Don't require a booted deployment

I'm working on a patch to add --sysroot support, and for testing
OSTree stuff I often work from a "traditional" host workstation, and
then I have OSTree content in /.

This makes "atomic status" just work for that; I simply have no booted
deployment.
Add: --sysroot and --os arguments

These match OSTree.  There are a variety of use cases here.  One is
for test suites; we can stand up a temporary sysroot directory, and
operate on content inside there.

Another is doing virtual machine upgrades offline from a host system,
or upgrading a different OS.

The duplication here is a bit unfortunate; if we add a lot more
commands we should revisit this and perhaps have a common option
group.