sign_official_build: Support signing additional RW firmware in shellball.
sign_official_build: Support signing additional RW firmware in shellball.

There will be more bios*.bin (ex, bios_rw.bin) in firmware updater, and we do
want to sign all files.

BRANCH=signer
BUG=chromium-os:35369
TEST=sign_official_build.sh ssd DEV_IMAGE ../../tests/devkeys

Change-Id: I2ea0c5c3d7a18c43df581f50b4bd907206dcd7ad
Reviewed-on: https://gerrit.chromium.org/gerrit/36890
Tested-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Reviewed-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Reviewed-by: Gaurav Shah <2987db6a10bcfe664554a372d01e80df7fd325a3@chromium.org>
Commit-Ready: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>

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