Fix signing script to work with new recovery image format.
Fix signing script to work with new recovery image format.

BUG=chrome-os-partner:1573
TEST=Manually tested with the latest signed release build. Recovery installer successfully completed and installed the image on the SSD.

Change-Id: I92706e957a1d339db516600ef0d86141d914b0d2

Review URL: http://codereview.chromium.org/4262004

coreboot/vboot,ccaapton/vboot_reference,ionave/seismograph,coreboot/vboot,ccaapton/vboot_reference,ionave/seismograph,ccaapton/vboot_reference,coreboot/vboot,marineam/seismograph,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,marineam/seismograph,acorn-marvell/vboot_reference,coreboot/vboot,ionave/seismograph,acorn-marvell/vboot_reference,marineam/seismograph,ccaapton/vboot_reference,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,marineam/seismograph