Update McastSenderTest/McastReceiverTest to bind the multicast sockets the same as JGroups

JGroups binds multicast sockets using specific MulticastSocket constructors depending on the operating system (to avoid crosstalk issues).

McastSenderTest and McastReceiverTest always bind the socket using the basic MulticastSocket(port) constructor.

In order to more closely test the way JGroups will be sending and receiving the packets, these tests will be updated to bind the sockets the same way.