crosperf: allow weight in cwp approximation larger than 1

This patch changed the check on the weight in cwp approximation mode.
The weight should be a float no less than 0.

BUG=chromium:924593
TEST=Tested with a simple experiment on eve.

Change-Id: Ia5ef804b5f11e36f6b5066fba6f40855bd716d2f
Reviewed-on: https://chromium-review.googlesource.com/1431272
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zhizhou Yang <zhizhouy@google.com>
Reviewed-by: Luis Lozano <llozano@chromium.org>
1 file changed