When on VMWare, strip the other 'gpu' dimension values.
When on VMWare, strip the other 'gpu' dimension values.

In the current server implementation, each dimension is a cost so it's better to
limit its number. So instead of having 'gpu': ['15ad' '15ad:0405', 'none'], it's
now just 'gpu': ['none'].

R=bpastene@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1740433004

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