Remove redundant default=None for config options
Remove redundant default=None for config options

The cfg module sets the default values as None by default. There
is no need to set this again.

The default is set as None:
http://docs.openstack.org/developer/oslo.config/opts.html#oslo.config.cfg.Opt

Change-Id: I5ab948b1571e51d05f6eb9f35720d0eecc3a56ab

zzicewind/oslo.log,dims/oslo.log,meganjbaker/oslo.log,magic0704/oslo.log,akash1808/oslo.log,openstack/oslo.log,JioCloud/oslo.log,varunarya10/oslo.log