This commit changes the sysroot API so that one can create arbitrary
new deployment checkouts, then commit them as one step. This is to
enable things like an automatic bisection tool which say create 50
deployments at once, then when done clean them up.
This also moves some printfs from the library into src/ostree.
Now that we have a real GObject for the sysroot, we have a convenient
place to keep track of 4 pieces of state:
* The current deployment list
* The current bootversion
* The current subbootversion
* The current booted deployment (if any)
Avoid requiring callers to pass all of this around and load it
piecemeal; instead the new thing is ostree_sysroot_load().
Originally, the idea was that clients would replicate "OS/tree"s from
a build server, but we'd run things like "ldconfig" on the client.
This was to allow adding e.g. the nVidia binary driver.
However, the triggers were the only thing in the system at the moment
that really had expected knowledge of the *contents* of the OS, like
the location of binaries.
For now, it's architecturally cleaner if we move the burden of
triggers to the tree builder (e.g. gnome-ostree or RPM). Eventually
we may want OSTree to assist with this type of thing (perhaps
something like RPM %ghost), but this is the right thing to do now.