restapi : storage_format option doesn't exists in 'add storagedomain' options

storage_format is not displayed as one of the available
options in cli for add storagedomain

Change-Id: I018dc2f003f0c8e449adb596412d8d797785efda
Bug-Url: https://bugzilla.redhat.com/961229
Signed-off-by: Ravi Nori <rnori@redhat.com>