test-webkitpy: split test-finding code into a different module

test-webkitpy: split test-finding code into a different module
https://bugs.webkit.org/show_bug.cgi?id=82253

Reviewed by Adam Barth.

Per suggestion from abarth, this change splits all the
filesystem-crawling, test-finding code in test-webkitpy out into
a separate module and switches to using a FileSystem object.
This makes things much more testable, so we also add tests :).

We also add a realpath() method to the Filesystem object, since
test-webkitpy needs that in order to be able to resolve symlinks
properly to determine whether a file is under a particular tree
or not.

* Scripts/webkitpy/common/system/filesystem.py:
(FileSystem.realpath):
* Scripts/webkitpy/common/system/filesystem_mock.py:
(MockFileSystem.realpath):
* Scripts/webkitpy/test/main.py:
(Tester.__init__):
(Tester.add_tree):
(Tester.run):
(Tester._run_tests):
(Tester._log_exception):
* Scripts/webkitpy/test/test_finder.py: Added.
(TestDirectoryTree):
(TestDirectoryTree.__init__):
(TestDirectoryTree.find_modules):
(TestDirectoryTree.find_modules.file_filter):
(TestDirectoryTree.to_module):
(TestDirectoryTree.clean):
(TestFinder):
(TestFinder.__init__):
(TestFinder.add_tree):
(TestFinder.additional_paths):
(TestFinder.clean_trees):
(TestFinder.is_module):
(TestFinder.to_module):
(TestFinder.find_names):
(TestFinder._exclude):
* Scripts/webkitpy/test/test_finder_unittest.py: Added.
(TestFinderTest):
(TestFinderTest.setUp):
(TestFinderTest.tearDown):
(TestFinderTest.test_additional_system_paths):
(TestFinderTest.test_is_module):
(TestFinderTest.test_to_module):
(TestFinderTest.test_clean):
(TestFinderTest.test_find_names):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@112168 268f45cc-cd09-0410-ab3c-d52691b4dbfc