lrdpv2: randomize t32 intercom port

Currently our generated t32 launcher script always uses port 20,000 for
intercom. This prevents end users from launching two instances of t32
without hacking up the config file by hand. Randomize the port number to
avoid this (there will still be a chance of collision, but it should be
negligible).

Change-Id: Ia6f63a69e0ed315ac08c58d9903c2d1ef34b6c69