Fixes related to mount failure path cleanup

b=17752
i=umka
i=shadow

lustre/obdclass/obd_mount.c

@@ -1111,6 +1111,7 @@ static int server_start_targets(struct super_block *sb, struct vfsmount *mnt)
         if (rc) {
                 CERROR("failed to start server %s: %d\n",
                        lsi->lsi_ldd->ldd_svname, rc);
+                server_deregister_mount(lsi->lsi_ldd->ldd_svname);
                 GOTO(out_mgc, rc);
         }