Register the volume_opts config options in remotefs.py

Register the volume_opts config options in remotefs.py

With commit bc23e0bf415defb1956c9864ac33390bb4cc2017 a new
volume_opts configuration option list was added into
cinder/volume/drivers/remotefs.py.  This new list, however,
was never registered.  When an options list is not registered
genconfig cannot figure out the right place to put the config
options and will fail to generate the sample file.

To resolve this, the patch simply registers the new options
list in remotefs.py.  Once the list is registered we are,
once again, able to generate the sample file.

Change-Id: Ic2bb95d7e2296d893f8acc5b3119f0be6a4b5c74