Connect TC2 to MySQL database at startup

Summary:
This is a follow-up for be5e31ed.

As the onload procedure is now used
for a non destructive task, commands
with crash risk are located to a new
'launch' proc.

Test Plan: .tcl onload

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1243