Move ostree-* executables to /usr/lib/ostree

Move ostree-* executables to /usr/lib/ostree

Why not to use libexecdir?

Because this directory does not exist on some distros or paths
between distros varies. There are several reasons why a well
known path is prefered, for example when generating a kernel
command line:

init=${ostree}/usr/lib/ostree-boot/ostree-prepare-root

In addition this saves us some typing in a console when wanting
to access the "ostree" cmd line.

Closes: #449
Approved by: cgwalters