Pad state dump

Because we append the function/line info after debug lines in the gate
logs, the pretty-print ends up not looking all that pretty.  Pad it.

Change-Id: Ice013428342614300cd51e8b7be56e79b75b31fc

diskimage_builder/block_device/blockdevice.py

@@ -107,8 +107,8 @@ class BlockDeviceState(collections.MutableMapping):
         # This is pretty good for human consumption, but maybe a bit
         # verbose.
         nice_output = pprint.pformat(self.state, width=40)
-        for line in nice_output.split('\n'):
-            logger.debug(" " + line)
+        for l in nice_output.split('\n'):
+            logger.debug('{0:{fill}{align}50}'.format(l, fill=' ', align='<'))
 
 
 class BlockDevice(object):