watchlist: Allow specified a bug to attach the watchlist info to.

watchlist: Allow specified a bug to attach the watchlist info to.
https://bugs.webkit.org/show_bug.cgi?id=69288

Reviewed by Eric Seidel.

* Scripts/webkitpy/tool/commands/applywatchlistlocal.py: Add support for bugid.
* Scripts/webkitpy/tool/commands/applywatchlistlocal_unittest.py:
Add tests and fix an existing test because the unit tests do not go through the
normal command line processing (so the -g argument remained when we determined bug ids).
* Scripts/webkitpy/tool/commands/commandtest.py: Change the derivation to
get the assert raises regex method.
* Scripts/webkitpy/tool/commands/download.py: Fix the command help to be more unixy.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96540 268f45cc-cd09-0410-ab3c-d52691b4dbfc