Use correct string format to get bisect confidence.

BUG=405541
NOTRY=true

Review URL: https://codereview.chromium.org/499653002

Cr-Commit-Position: refs/heads/master@{#291524}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291524 0039d316-1c4b-4281-b951-d872f2087c98

tools/bisect-perf-regression.py

@@ -199,7 +199,7 @@ Status: %(status)s
 Test Command: %(command)s
 Test Metric: %(metrics)s
 Relative Change: %(change)s
-Estimated Confidence: %(confidence)d%%"""
+Estimated Confidence: %(confidence).02f%%"""
 
 # The perf dashboard specifically looks for the string
 # "Author  : " to parse out who to cc on a bug. If you change the