[mount] Restore @home subvolume

In 942221c764 the fixed-setup
(with /@ and /@home) was replaced by the configurable btrfs
layout, but the default went away. Restore the two-subvolume
layout if nothing is configured.

src/modules/mount/main.py

@@ -42,7 +42,7 @@ def get_btrfs_subvolumes():
     if btrfs_subvolumes is None:
         libcalamares.utils.warning("No configuration for btrfsSubvolumes")
     if not btrfs_subvolumes:
-        btrfs_subvolumes = [ dict(mountPoint="/", subvolume="/@") ]
+        btrfs_subvolumes = [ dict(mountPoint="/", subvolume="/@"), dict(mountPoint="/home", subvolume="/@home") ]
 
     return btrfs_subvolumes