Avoid use xx=[]  for parameter initial value
Avoid use xx=[]  for parameter initial value

Use xx = [] for the parameter initial value, this parameter will
only be initialized at the first call, this is should be avoided.
Better choice is to set the initial value to None, then the initialization
time use xx= xx or []

more information:http://effbot.org/zone/default-values.htm

Change-Id: Ia89b9741731c07d8bf08691a1c6544742625cad6

openstack/python-troveclient,Tesora/tesora-python-troveclient,openstack/python-troveclient,Tesora/tesora-python-troveclient