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/lib/ply/yacc.py

@@ -195,6 +195,8 @@ class YaccProduction:
         self.lexer = None
         self.parser= None
     def __getitem__(self,n):
+        if isinstance(n,slice):
+            return [self[i] for i in range(*(n.indices(len(self.slice))))]
         if n >= 0: return self.slice[n].value
         else: return self.stack[n].value