engine: Adding no-arg constructor to gluster parameters

Added a no-arg constructor to all gluster parameters. This
is to make sure these parameter classes are added to GWT
serialization policy whitelist.

Change-Id: I4ab197e9fb8f9d8f7f0be021716a6b3a028f1546
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>