Fix pylint error

************* Module freezer.engine.rsync.pyrsync
freezer/engine/rsync/pyrsync.py:135:53: E0601: Using variable 'tailsize' before assignment (used-before-assignment)

Change-Id: I86763ae9715fe9ddef483f136c40a3bb8df8a459

freezer/engine/rsync/pyrsync.py

@@ -87,6 +87,7 @@ def rsyncdelta(datastream, remotesignatures, blocksize=4096):
     match = True
     matchblock = -1
     last_byte = []
+    tailsize = 0
     while True:
         if match and datastream is not None:
             # Whenever there is a match or the loop is running for the first