The socket will now listen for messages recieved from the monitor
process.
Currently there are three messages supported.
* startHeapProfiling
* stopHeapProfiling
* requestHeapProfile
When the process recieves these messages, the relevant RTS API functions
are called.
This commit also includes a new python test driver, and support for test
scripts which can communicate over the socket.
If you are manually starting the sockets (ie, before hs_main runs) then
you need to call `eventlog_socket_ready()` before attempting to use the
control channel, to signal that the RTS is ready to receive requests.
I also have rewritten the testsuite driver into python to allow testing
the control socket by sending various messages.
There is now a test matrix which tests normal/reconnect modes for
fibber/fibber-tcp/fibber-c-main against all the control scripts.