New method to compute md5 hash of file

Signed-off-by: Vojtech Trefny <vtrefny@redhat.com>

blivet/util.py

@@ -9,6 +9,7 @@
 import sys
 import tempfile
 import uuid
+import hashlib
 from decimal import Decimal
 from contextlib import contextmanager
 
@@ -357,6 +358,18 @@ def insert_colons(a_string):
     else:
         return suffix
 
+def md5_file(filename):
+
+    md5 = hashlib.md5()
+    with open(filename, "rb") as f:
+
+        block = f.read(65536)
+        while block:
+            md5.update(block)
+            block = f.read(65536)
+
+    return md5.hexdigest()
+
 class ObjectID(object):
     """This class is meant to be extended by other classes which require
        an ID which is preserved when an object copy is made.