Rewrite gen_fuzz_test_cases.sh script to use new signing utilities.
Rewrite gen_fuzz_test_cases.sh script to use new signing utilities.

TEST=Generated images verify successfully using right keys.

Review URL: http://codereview.chromium.org/2836036

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