Bug 975386 - Fix intermitten failure for test_settings_change_keyboard_l...

...anguage.pyFix for test_settings_change_keyboard_language.py.

Added a wait for the newly added keyboard to appear in the list.

Ran an adhoc with this test and it passed http://qa-selenium.mv.mozilla.com:8080/job/b2g.hamachi.mozilla-central.ui.adhoc/225/