Make upload.py treat images as binaries, so they upload correctly and display in Reitveld.

BUG=227346

Review URL: https://chromiumcodereview.appspot.com/14820015

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@198833 0039d316-1c4b-4281-b951-d872f2087c98