Make vbutil_keyblock handle unsigned blocks. Also enable --unpack option and
add tests for it.
Modify vbutil_kernel to allow unsigned keyblocks, correct usage message,
and fix the --debug option which was somehow disabled.
Update load_kernel_test to accept /dev/null for the public key, to test
non-signed kernel keyblocks.
Review URL: http://codereview.chromium.org/3124004
Also renamed verify preamble functions, now that they do not need the
'2' at the end to differentiate them from the now-deleted original
implementation.
BUG=4501
TEST=Ran make runtests; all pass.
Review URL: http://codereview.chromium.org/3027009
