Use swap mountpoint

Having swap set at "none" makes hibernating not possible.
AFAIK, no filesystem/partition sets mountpoint as "none" nor has any other besides swap an empty mountpoint at the stage where the fstab module is called.
Tests so far show this change creates a working fstab when using a swap partition.

src/modules/fstab/main.py

@@ -129,7 +129,7 @@ class FstabGenerator(object):
 
         return dict(
             device="UUID=" + partition["uuid"],
-            mount_point=mount_point or "none",
+            mount_point=mount_point or "swap",
             fs=fs,
             options=options,
             check=check)