sysroot: Track whether /run/ostree-booted exists

Prep for further work around deployment staging.

Closes: #1497
Approved by: jlebon

src/libostree/ostree-sysroot-private.h

@@ -50,6 +50,7 @@ struct OstreeSysroot {
   GLnxLockFile lock;
 
   gboolean loaded;
+  gboolean ostree_booted;
 
   gboolean is_physical; /* TRUE if we're pointed at physical storage root and not a deployment */
   GPtrArray *deployments;