Add a test that "apitrace diff-images" flags mismatching images.

Add a test that "apitrace diff-images" flags mismatching images.

With this test we add a new EXPECT_FAILURE: attribute to the script
syntax to indicate that a particular apitrace command in the script is
expected to fail. This requires manually invoking the Popen
constructor rather than using subprocess.check_output, (which is
*close* to what we need but fails to assign the output when raising an
exception).

We also remove the globbing from the CMakeLists.txt file to get a
manual ordering of the tests (rather than executing in alphabetic
order).