Provide a runs.insecurely to be used with test variants
Use cases involving running of test suites and doc generation require
more liberal ownership and read/write permission to application files.
When runs.insecurely is set to true, the effective runtime user will
be lives.as, the same user that owns the application files and
D999 is a complement to this change to allow restrictions on this and
other potentially sensitive configuration.
Depends on D999, D1002
Test Plan: Run go test ./....
Reviewers: thcipriani, mmodell, hashar, Release-Engineering-Team, demon
Reviewed By: thcipriani, Release-Engineering-Team
Differential Revision: https://phabricator.wikimedia.org/D1003