Testing the ivi_layout API requires two things:
- the tests must be written as a controller module to access the API
- the tests need a helper client to create some objects that can then be
  managed via the API

This patch adds all the infrastructure and two different kinds of
example tests.

Internal ivi-shell (ivi_layout) API tests are listed as ivi-*.la files
in TESTS in Makefile.am. Weston-tests-env detects these, and runs Weston
with ivi-shell, and loads the given module as a controller module, not
as a normal plugin.

The test controller module ivi-*.la will launch a helper client. For
ivi-layout-test.la the helper client is ivi-layout.ivi.

The helper client uses the weston-test-runner framework to fork and exec
each TEST with a fresh connection to the compositor.

The actual test is triggered by the weston_test_runner protocol
interface, a new addition to weston-test.xml. The helper client uses
weston_test_runner to trigger a test, and the server side of the
interface is implemented by the test controller module
(ivi-layout-test.la).

The server side of weston_test_runner uses the same trick as
weston-test-runner.h to gather a list of defined tests. A test is
defined with the RUNNER_TEST macro.

If a test defined by RUNNER_TEST succeeds, an event is sent to the
helper client that it can continue (or exit). If a test fails, a fatal
protocol error is sent to the helper client.

Once the helper client has iterated over all of its tests, it signals
the batch success/failure via process exit code. That is cought in the
test controller module, and forwarded as Weston's exit code.

In summary: each ivi_layout test is a combination of a client side
helper/setup and server side actual tests.

v2: Load weston-test.so, because create_client() needs it.

v3: add a comment about IVI_TEST_SURFACE_ID_BASE.

v4: Rebased to upstream weston-tests-env changes.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com> (v2)