Simplify setup of a proxy-only or broker-only SDP server.
The Helix Installer is useful for setting up a host that is to
be used only for a p4p or p4broker process, but it doesn't do
the job completely, and also leaves around cruft.
Some things that need doing:
* For a proxy, create the /p4/N/cache directory and symlink.
* Removed a bunch of stuff only needed when a P4D server is
run, .e.g P4ROOT. There should still be /p4/N/logs and
/p4/N/tmp directories, but not root, offline_db, depots, and
* For a proxy, generate a crontab with call to p4pcm.pl.
* For a broker, generate a crontab with call to broker_rotate.sh.