Add a wait to bolster the test

Changed locator for outgoing call number
Xfailing test_call_contact due to contact name no longer appearing on call screen

This test has been failing on CI since May 3rd. I have made two fixes to the test which bolster it and allow it to pass to a certain point, but it still fails as the behaviour of the call screen seems to have changed. The contact name no longer appears on the screen. I have opened https://bugzilla.mozilla.org/show_bug.cgi?id=869060 regarding that issue.