Bug 1041565 - Setting for toggling pseudolocales

https://bugzilla.mozilla.org/show_bug.cgi?id=1041565
`waitForElementToDisappear` is used when there is already an element in the DOM tree, then after a while, you called an asyc call or anything to make the element disappear.

But in your scenario, there is no such element at first, so marionette-js would try to **wait** until the element is showing up before timeout and that's why this would make your test run so long. 

A better (hackish) way coming from my mind is to find `select` (it will always be there) and check its children to see whether such option did exist or not. 

WDYT ?