[telemetry] Add --recover-from-unknown-page-exceptions option

This is useful when running large page sets where flake is an acceptable
outcome.

R=tonyg

Review URL: https://codereview.chromium.org/108953004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239782 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239782