Unxfail test_settings_cell_data.py

Add wait to bolster the test

This test has been passing regularly lately [1]. Just some fails due to broken pipes, but also some fails related to the carrier name [2], for which I've added a wait.

```v1.0.1``` -> merge
```v1-train``` -> test and merge
```master``` -> test and merge

[1] http://qa-selenium.mv.mozilla.com:8080/view/B2G%20Inari/job/b2g.inari.gaia.v1.0.1.ui.xfail.ril/192/testReport/junit/%28root%29/TestSettingsCellData/history/?
[2] http://qa-selenium.mv.mozilla.com:8080/view/B2G%20Inari/job/b2g.inari.gaia.v1.0.1.ui.xfail.ril/219/testReport/junit/%28root%29/TestSettingsCellData/test_enable_cell_data_via_settings_app/?