Fix error on paste create via conduit

Summary: default policy to most liberal policy available for the installation

Test Plan: echo "sup man?" | arc paste Was able to view resultant paste with no errors!

Reviewers: epriestley, vrana

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1815

Differential Revision: https://secure.phabricator.com/D3548