Reorder rootfs partitions to be spinning disk friendly.

Change the order of partitions to given better performance for spinning disks.
However, this change affects all devices, not just those with spinning disks.

We will be able to remove the per-board overrides from several devices if/
when this change is accepted.

BUG=chromium-os:38122
TEST=image_to_live, (Will run trybots, and perform a recovery).

Change-Id: Ibe60e384e0392936f9f8ceb326618951367974df
Reviewed-on: https://gerrit.chromium.org/gerrit/41792
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>

build_library/legacy_disk_layout.json

@@ -68,13 +68,6 @@
         "type":"efi",
         "blocks":"32768"
       },
-      {
-        "num": 1,
-        "label":"STATE",
-        "type":"data",
-        "blocks":"2097152",
-        "features":["expand"]
-      },
       {
         "num": 5,
         "label":"ROOT-B",
@@ -88,6 +81,13 @@
         "type":"rootfs",
         "blocks":"4194304",
         "fs_blocks":"262144"
+      },
+      {
+        "num": 1,
+        "label":"STATE",
+        "type":"data",
+        "blocks":"2097152",
+        "features":["expand"]
       }
     ],
     "usb": [