Bug 1096915 - Add a test to re-dial the last MO number by pressing the c...

...all button twice
We should update this condition, now the callscreen displays 22 digits. By the way, I think the constant should be put in the Page object as a Class constant.

I filed [bug 1104645](https://bugzilla.mozilla.org/show_bug.cgi?id=1104645) for that.