bitbake: bitbake: Convert to python 3

Various misc changes to convert bitbake to python3 which don't warrant
separation into separate commits.

(Bitbake rev: d0f904d407f57998419bd9c305ce53e5eaa36b24)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake-dumpsig

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # bitbake-dumpsig
 # BitBake task signature dump utility
@@ -23,6 +23,7 @@ import sys
 import warnings
 import optparse
 import logging
+import pickle
 
 sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(sys.argv[0])), 'lib'))
 
@@ -51,7 +52,6 @@ options, args = parser.parse_args(sys.argv)
 if len(args) == 1:
     parser.print_help()
 else:
-    import cPickle
     try:
         output = bb.siggen.dump_sigfile(args[1])
     except IOError as e: