frontend: RDP doesn't pass clipboard

This patch enables RDP clipboard passing.

Change-Id: I01a07345a45f344a3218860bde023532e40d46c4
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=909270
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>