Set default token provider to UUID

This changes the default token provider to UUID, which affords a much
better deployer experience (no external dependencies and no additional
setup complexity) for deployers. It also provides a better end-user
experience (smaller, more manageable tokens) and appears to be the more
popular deployment option today, despite the current default to PKI.

DocImpact
Closes-Bug: 1350000

Change-Id: I7fb2b191cce7a9762c33fee09e7e8d48a71a297b
Merge "Set default token provider to UUID"