Rename animations/animation-direction-reverse.html to animations/animation-direction-reverse-fill-mode-pause.html

This will allow us to rename the other direction-reverse tests to use a more
consistent scheme.

R=dstockwell

Review URL: https://codereview.chromium.org/34253002

git-svn-id: svn://svn.chromium.org/blink/trunk@160275 bbb929c8-8fbe-4397-9dbb-9b2b20218538