runner: Use socket communications

Set up a socket and pass it to the tests. Dump received communications
to disk.

When generating results.json, use socket comms if it exists.

Signed-off-by: Petri Latvala <petri.latvala@intel.com>
Cc: Arkadiusz Hiler <arek@hiler.eu>
Acked-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>