centralize getting the hash because duh

grml.py

@@ -10,7 +10,6 @@
 
 import datetime
 import json
-import hashlib
 import os
 import re
 ##
@@ -94,17 +93,14 @@ class Updater(_base.BaseUpdater):
         if ver_info.get('arch') != self.arch:
             self.do_update = True
             self.force_update = True
-        try:
-            hasher = hashlib.new(self.hash_type)
-            with open(self.dest_iso, 'rb') as fh:
-                hasher.update(fh.read())
-            if self.old_hash != hasher.hexdigest().lower():
-                self.do_update = True
-                self.force_update = True
-        except FileNotFoundError:
+        if not os.path.isfile(self.dest_iso):
             self.do_update = True
             self.force_update = True
             return(None)
+        realhash = self.getISOHash()
+        if self.old_hash != realhash:
+            self.do_update = True
+            self.force_update = True
         return(None)
 
     def getNewVer(self):