futility: add support for .pem with public key

Add support for PEM file containing a RSA Public key in futility "show"
and "create" commands.

When "futility create" is given a PEM file with only a RSA public key,
generate the proper .vbpubk2 rather than failing.

TEST=make runtests
and run manually
futility show tests/testkeys/key_rsa4096.pub.pem
futility show tests/testkeys/key_rsa4096.pem

Change-Id: I707ceca54c80ba21f53869ad86c86fa23b31e665
Reviewed-on: https://chromium-review.googlesource.com/306683
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
8 files changed