make_dev_ssd: new script to change SSD image to dev key

The make_dev_ssd.sh is made for devinstall shim to
change SSD kernels to be signed by dev keys.

 - Kernel A, B will be resigned with dev keys (ignore if A/B seems not bootable)
 - Adding param --remove_rootfs_verification can even disable rootfs hash check

This CL also includes some shared refine/fix to make_dev_firmware.sh

BUG=chrome-os-partner:1276
TEST=sudo ./make_dev_ssd.sh; (seeing Kernel A is resigned and B is ignored)
     then reboot without developer mode (OK),
          rootdev shows /dev/dm-0, rootdev -s shows /dev/sda3
     sudo ./make_dev_ssd.sh --remove_rootfs_verification;
     then reboot without developer mode (OK), rootdev shows /dev/sda3

Change-Id: Ic20f734b2af42e50a43c19a565a166a39d57a7fd

Review URL: http://codereview.chromium.org/3772013
4 files changed