Add a customize_image script.
Add a customize_image script.

For now, it just updates the root password.

BUG=5080
TEST=ran the script,tried the image

Review URL: http://codereview.chromium.org/3061045

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