Add variant blivet 'part_fs' needle, rename the other

When running universal tests with a non-Server image, which is
not common but *does* happen (e.g. manually built test image),
the pre-selected filesystem in blivet-gui will be ext4 not xfs
(just as with custom partitioning). So we need xfs and ext4
variants of this needle. Renamed the XFS one for consistency.

needles/anaconda/partitioning/blivet/anaconda_blivet_part_fs_ext4_selected-20170512.json

@@ -0,0 +1,17 @@
+{
+  "properties": [],
+  "area": [
+    {
+      "xpos": 337,
+      "ypos": 394,
+      "type": "match",
+      "width": 167,
+      "height": 24
+    }
+  ],
+  "tags": [
+    "LANGUAGE-english",
+    "anaconda_blivet_part_fs",
+    "anaconda_blivet_part_fs_ext4_selected"
+  ]
+}