fix(BinaryLogClient): use writeBuffered exclusively & adjust packetNum for SSL switch auth

[glarwood]

The changes introduced in #272 by @osheroff were not quite enough for me to connect to Azure MySQL. Testing against two different Azure MySQL DB's, I found that we needed to use PacketChannel#writeBuffered for each command.

Additionally, for connections using an SSL socket, the packet number needed to be doubly incremented in between the AuthenticateCommand packet and the AuthenticateNativePasswordCommand packet. This is presumably because of an implicit SSL packet being sent by the socket before the issuing of the AuthenticateNativePasswordCommand packet.

I've tested against standard MySQL databases versions (5.7) and found no problems exclusively using PacketChannel#writeBuffer both with/without SSL. I'll test it out with a few other versions and report back. @shyiko, do you anticipate any issues using PacketChannel#writeBuffer in the general case?

[shyiko]

Thanks Gabriel. This is great!
The only concern that I have is that removing

public void write(Command command, int packetNumber) throws IOException
public void write(Command command) throws IOException

from PacketChannel is a breaking change (I'll take care of it).
Merging in 🙇‍♂️

[shyiko]

@glarwood 0.20.1 uploaded to Maven Central.