Add a sleep to the keyboard app's send method to deal with new el.tap() timing

This addresses the failure on CI as seen at http://qa-selenium.mv.mozilla.com:8080/view/B2G%20Inari/job/b2g.inari.gaia.v1.0.1.ui.ril/11/testReport/junit/%28root%29/TestSettingsPasscode/test_set_passcode_by_settings/