This will no longer be static soon.

Ref: #10818

Some recent refactoring made these export no longer necessary. Also,
stop displaying the Unix socket paths at startup since there will soon
be many of them and they're not that interesting.

Ref: #10818

There will soon be multiple log directories so the paths will no longer
be static in runtests.pl. Also, get rid of $SERVER2IN which was not
used.

Ref: #10818

This sets up the runner environment to start running tests.

Ref: #10818

This is where citest_starttest is called.

Ref: #10818

Program arguments are marshalled and then written to the end of a pipe
which is later read from and the arguments unmarshalled before the
desired function is called normally.  The function return values are
then marshalled and written into another pipe when is later read from
and unmarshalled before being returned to the caller.

The implementation is currently blocking but can be made non-blocking
without any changes to the API.  This allows calling multiple runners
without blocking in the future.

Ref: #10818

This allows it to run in a non-blocking manner.

Ref: #10818

When the -j option is given, a new process is spawned in which the test
programs are run and from which test servers are started. Only one
process can be started at once, but this is sufficient to test that the
infrastructure can isolate those functions in a new task. There should
be no visible difference between the two modes at the moment.

Ref: #10818
Closes #11064

The controller currently only creates and uses one, but more are now
possible.

Ref: #10818