Iterate over copy of sys.modules keys in Python2/3
Iterate over copy of sys.modules keys in Python2/3

Iterate over a copy of sys.modules keys in both Python 2.x and
Python 3.x.  In Python 3.x, keys() is not a copy, and therefore
items can't be popped from it while iterating.

Change-Id: I98c3d7695bbfe3a6a4f23990af45a07dc147f22f
Closes-Bug: #1463503

sdpp/python-keystoneclient,magic0704/python-keystoneclient,Mercador/python-keystoneclient,klmitch/python-keystoneclient,sdpp/python-keystoneclient,magic0704/python-keystoneclient,klmitch/python-keystoneclient,Mercador/python-keystoneclient