Merge libmounts into libotautil.

Export its header (mounts.h) from there, and drop the dot dot dependency
from libupdater / updater.

Test: mmma bootable/recovery
Test: recovery_component_test
Change-Id: Ic26a6b9b78a34dbe1f178b138f3abaafffbec44c
diff --git a/roots.cpp b/roots.cpp
index 8907bbd..26ebf1f 100644
--- a/roots.cpp
+++ b/roots.cpp
@@ -39,7 +39,7 @@
 #include <ext4_utils/wipe.h>
 #include <fs_mgr.h>
 
-#include "mounts.h"
+#include "otautil/mounts.h"
 
 static struct fstab* fstab = nullptr;