filechooserbutton: For tests, wait for signals instead of just sleeping
filechooserbutton: For tests, wait for signals instead of just sleeping

This should let tests complete faster.  Also, this will let us test
that the correct signals are actually being emitted.

The tests now fail, as the signals are not being emitted when they
should.

Signed-off-by: Federico Mena Quintero <4999915a961edfd7686112c2935288e1266eae14@gnome.org>

Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2