Add ability to abort server sockets via bttestui

This equalizes the behavior of the Close and Abort button. Abort will
disconnect the local client socket as well as all sockets which were
established via the listening server socket.

Change-Id: I68d3d7190641aab44612fa3fc00b38fdc31799a3
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>