"veyron2/security": BlessingRoots and BlessingStore (part 2)

This CL hooks up BlessingRoots and BlessingStore into Principal.
It also adds additional methods to security.Context as defined
in the new security model.

Change-Id: I3aaf15fd1ded186c0fd57163f9b22806a68d65a3
12 files changed
tree: 97bc018e2ba2155463f1b9858351b1ca6e9e8d00
  1. lib/
  2. profiles/
  3. runtimes/
  4. security/
  5. services/
  6. tools/