No bug. Check key before deleting. r=aki

--HG--
extra : rebase_source : 81730147cf82856d57efb8d2e8414cbd5e5dd95b
Bug 829211 - Use mozpool and mozharness for the Android pandas r=aki
Bug 910449 - Use b2g-bin instead of b2g, if it exists, r=davehunt
Bug 917225 - Add --restart to gaia-ui-tests, r=davehunt