check for xtfsutil before executing verification

xtreemfs_client/verify.py

 import os
 import subprocess
 
+import div_util
+import OSDManager.ExecutableNotFoundException as ExecutableNotFoundException
+
 '''
 verify a tile folder: check whether all files in its subdirectories 
 (representing scenes) are located on the same OSD.
@@ -35,6 +38,8 @@ gmsFolder/utmStripes/utmTiles/scenes/files
 
 
 def verify_gms_folder(gms_folder, verbose=False):
+    if not div_util.check_for_executable('xtfsutil'):
+        raise ExecutableNotFoundException("No xtfsutil found. Please make sure it is contained in your PATH.")
     layout_is_correct = True
     for utmStripe in os.listdir(gms_folder):
         if not os.path.isdir(gms_folder + "/" + utmStripe):