As discussed on blink-dev, we will start checking in the imported w3c tests directly.

This is patchset 1 of 4 in making that happen.

This patch changes update-w3c-deps to do the import. Tests will now be imported into the "LayoutTests/imported" directory, to avoid any conflicts with the old git repos.

This patch significantly reworks update-w3c-deps, and patches webkitpy.test_importer to remove the import logs, make logging work better during the import, and handle skipping subdirs properly when not importing in place.

This patch also adds an exit() method to the SystemHost class to remove one more reason for importing sys.

TBR=eseidel@chromium.org
BUG=413454
BUG=

Review URL: https://codereview.chromium.org/565673006

git-svn-id: svn://svn.chromium.org/blink/trunk@181860 bbb929c8-8fbe-4397-9dbb-9b2b20218538