connectivity: avoid TLS handshake loop

Two points are changed in this patch:
+ In peer_channel, the wait return broken_pipe (because if stopped
it's like the write operation, the socket behind is being removed).
Moreover, sending E_INTERRUPTED while in the handshake will cause
gnutls to loop in server_hello.
+ In ConnectionManager, if the ICE is negotiated and started (which
can be the case for a server because the client will start to negotiate
and send the answer on the DHT, so negotiation can finish before getting
remote peers) we cancel the waitForResponse timer to avoid any cancellation
while in the handshake.

GitLab: #519
Change-Id: I530d9eba47aa918c90b6a151061556f4af636fb5