factory_test_tools: provide more helpful debug messages

We often see key verification error in factory process,
but lack of detail information for what's heppening.

This CL attempts to add more messages when the verifiaction failed, especially
for dev-signed / recovery-signed issue.

TEST=./gft_verify_keys.sh /dev/sda2 bios.bin # seeing DEV-SIGNED IMAGE warning
     ./gft_verify_keys.sh /dev/sda4 devbios.bin # seeing DEV ROOTKEY warning
     ./gft_verify_keys.sh /dev/sda2 devbios.bin # seeing DEV-SINED, RECOVERY, DEV-ROOTKEY warnings

Change-Id: Ic7e09e15c4a0ad7a908e4d1c114990160e85704d


Review URL: http://codereview.chromium.org/6883039
1 file changed