Fix: test: lttng kernel modules still loaded after running test_clock_override

Fix: test: lttng kernel modules still loaded after running test_clock_override

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

After running test_clock_override, some lttng modules are still loaded.

$ lsmod | ag lttng
  lttng_test             32768  0
  lttng_tracer         2326528  1 lttng_test
  lttng_statedump       749568  1 lttng_tracer
  lttng_wrapper          16384  2 lttng_statedump,lttng_tracer
  lttng_uprobes          16384  1 lttng_tracer
  lttng_kprobes          16384  1 lttng_tracer
  lttng_lib_ring_buffer    61440  1 lttng_tracer
  lttng_kretprobes       16384  1 lttng_tracer
  lttng_clock_plugin_test    16384  1
  lttng_clock            16384  2 lttng_tracer,lttng_clock_plugin_test

Cause
=====

The order in which the modules are removed is important.

In `test_clock_override_timestamp` the last `modprobe --remove order` is

  modprobe --remove lttng-clock-plugin-test lttng-clock lttng-test

While other callsites order is:

  modprobe --remove lttng-test lttng-clock-plugin-test lttng-clock

Solution
========

Use

  modprobe --remove lttng-test lttng-clock-plugin-test lttng-clock

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I528df2e3e90664433337a547a74cdbe476d4ee62