The best practice in Python is not to use mutable object (i.e. list,
dictionary, or instances of most classes) as value of default argument.
See: https://docs.python.org/2/tutorial/controlflow.html#default-argument-values
This patch also added a hacking rule to enforce this practice.
Change-Id: I4aa8aede57d6fd31b4b30c3f7535b819e591165d
Closes-Bug: 1471349