cmd/principal: addtoroots can now be used to add (key, blessingpattern)
pairs directly (without a blessing).

I intend to use this in the prod-services test, where I will fetch
the public key via HTTP and then add to the roots of programs used
to talk to production services.

Change-Id: I49563b22ac8912f692a5929015f039f5c0062b54
4 files changed