[Telemetry] Make measurement smoke test error more useful

BUG=
NOTRY=True

Review URL: https://codereview.chromium.org/191973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255849 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255849