Auto-generate directory indexes for run-blink-httpd.

Also, automatically create the output directory if it doesn't exist.
Both of these changes are regressions caused by the switch from
lighttpd to apache (and other cleanups).

R=morrita@chromium.org
BUG=347341

Review URL: https://codereview.chromium.org/182533002

git-svn-id: svn://svn.chromium.org/blink/trunk@168057 bbb929c8-8fbe-4397-9dbb-9b2b20218538