Add support for using separate developer firmware keyblock while signing.

Add support for using separate developer firmware keyblock while signing.

Also re-factor the key generation script to its own directory, including wrappers for generating key pairs and keyblocks without needing to start keyset generation process from scratch. (Useful for generating new kernel keyblocks, and for retroactively adding new keys to an existing keyset - as in this case). 

Finally, change hard coded algorithm ids and keyblock modes to bash variables, for each changes and telling keyset configuration from a glance.

BUG=chrome-os-partner:2218
TEST=manually tried the following:
1) Generating an entire new keyset.
2) Generating a new key pair and creating a keyblock from an existing key (for generating dev firmware keyblock for existing PVT keysets)
3) Firmware signing via sign_official_build.sh of an image with a firmware payload/

Change-Id: I4e9bb96ac7e5fe4cc0d95af6162ad6d37bbd4bda

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=5746845

[Randall Spangler, 2011-03-02 22:27:43]

LGTM