ref/cmd/principal: Some principal getter additions.

As per https://github.com/veyron/release-issues/issues/991.

This CL adds:
(1): 'principal get recognizedroots' prints the recognized public keys and
     patterns.
(2): 'principal get peermap' prints the blessings to present to peers.
(3): --name and --rootkey flags to the 'get forpeer' and
     'get default' commands that prints either the name or the rootkey
     of the blessing.

Change-Id: Ib56161f66a2a5e7e736b0234f25a84555602bc31
8 files changed