Change ListOpt default value from str or None to list

In keystone/common/config.py, some ListOpt config object was inited
with a string or None default value, it's incorrect. This patch modifies
their default value to list objects.

Change-Id: I2aec4f49d94e131d45f7dc9bfeb63b8d819d0bb1
Closes-Bug: #1259735
Merge "Change ListOpt default value from str or None to list"