Don't use default=None for config options
Don't use default=None for config options

In the config module default=None is set as the default value,
so it isn't necessary to set it again when doing config options.

Change-Id: I09989ab679d249a9f7dea6af5d53c14dd1726e09
Closes-Bug: #1323975
CloudByteStorages/openstack,CloudByteStorages/openstack,yogeshprasad/openstack,yogeshprasad/openstack