tests: group structures tests in their own directory
The phpunit root directory has two test file:
AutoLoaderTest.php
StructureTest.php
The later was registered in phpunit under the `structure` test suite
while the former was not registered and hence never run (bug 47750).
This patch moves both files under the `structure` subdirectory and
change the suite to look in that directory. That will avoid us having
to manually maintain a list of test files.
Updated the __DIR__ in StructureTest.php.
Change-Id: I419c9157f32bdf7e1ff26a42f4bb3f3922b7be37