Use separate install-deps instructions for Red Hat 5 vs. 6
Add manual.test/loadtest.js

This script is much lighter weight than phantomjs because it doesn't
actually execute any javascript; it just makes HTTP and WebSocket
requests in the same way a real client would during startup.

Therefore this script can saturate a shiny-server instance using a
single client machine/VM.

There does seem to be a limit on how many sessions can be launched
at once before a single loadtest.js instance fails; on my dev machine
with ulimit -n 2000 it is about 260-270.