Merge pull request #1487 from grom-42/fix-send-pkt

Fix test on invalid null will topic value in connect packet

Fix test on invalid reserved bit value in connect packet

Add send of pubcomp in 02-subpub-qos2 script. To keep the broker session working while launching several tests on the same broker, the last packet of this transaction must be sent.

Fix way of sending packets in compliance tests. According to the documentation of python 3 socket::send method (https://docs.python.org/3/library/socket.html#socket.socket.send), the call to send must be retry until all data is sent while sending packet with a "large" amount of data.