update struct names and struct fiels

it wont be meaningful to call cephfs.NewcephfsDriver()
to get a new driver, it will be better if we call
cephfs.GetNewDriver() which returns the cephfs driver
object.

same goes for rbd also

Signed-off-by: Madhu Rajanna <mrajanna@redhat.com>

cephfs/main.go

@@ -57,7 +57,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	driver := cephfs.NewCephFSDriver()
+	driver := cephfs.NewDriver()
 	driver.Run(*driverName, *nodeID, *endpoint, *volumeMounter, cp)
 
 	os.Exit(0)