Tests: Use serial runner

Tests: Use serial runner

Observed issue
==============

Running `make check -jN` with N greater than 1 will fail a number of
different checks.

Cause
=====

The majority of the tests aren't designed to work in
isolation (e.g. using `LTTNG_HOME` and `LTTNG_RUNDIR`), and some tests
that exercise global system resources (e.g. kernel modules) will never
work reliably in parallel.

Solution
========

Create a serial test runner that can execute all the tests that
require global resources while the other tests that are defined as
'safe to parallelize' can be run concurrently.

Known drawbacks
===============

None.

Change-Id: I0b87d2cd5e870ee7f9241ec78390ed96a01efb38
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>