Sasl plain handshake

[Alkorin]

This PR contains #748 + a bug fix.
#748 calls sendAndReceiveSASLPlainHandshake two times leading to a runtime error:

INFO[0008] client/metadata fetching metadata for all topics from broker ***:9093
INFO[0008] Successful SASL handshake
fatal error: runtime: out of memory

After removing the call in Open, everything works fine:

INFO[0002] client/metadata fetching metadata for all topics from broker ***:9093
INFO[0002] Successful SASL handshake
INFO[0002] SASL authentication successful with broker ***:9093:4 - [0 0 0 0]
INFO[0002] Connected to broker at ***:9093 (unregistered)
INFO[0002] client/brokers registered new broker #2 at ***:9093
INFO[0002] client/brokers registered new broker #5 at ***:9093
INFO[0002] client/brokers registered new broker #7 at ***:9093
INFO[0002] client/brokers registered new broker #1 at ***:9093
INFO[0002] client/brokers registered new broker #3 at ***:9093
INFO[0002] Successfully initialized new client

[Alkorin]

Hi, any news ?
We would like to avoid having our own fork :/

[eapache]

Sorry for the delay on this. I manually rebased, tweaked and merged this.