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

src/boot/mkinitcpio/ostree

@@ -1,8 +1,8 @@
 #!/bin/bash
 
 build() {
-    add_binary /usr/sbin/ostree-prepare-root
-    add_binary /usr/sbin/ostree-remount
+    add_binary /usr/lib/ostree/ostree-prepare-root
+    add_binary /usr/lib/ostree/ostree-remount
 
     add_file /usr/lib/systemd/system/ostree-prepare-root.service
     add_symlink /usr/lib/systemd/system/initrd-switch-root.target.wants/ostree-prepare-root.service \