Update GPU dimensions to be unicode.
Update GPU dimensions to be unicode.

This reduces the number of str/unicode differences in unit tests. While this
works, when there's a diff in self.assertEqual(), the str/unicode difference
makes the diff much harder to read.

R=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1284263003 .

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py