cancel connection when acquired by BinLogStream

[oussama]

Currently when a BinLogStream is acquired it doesn't decrease the counter on the Pool, which causes the pool panic when it is dropped

[galeaspablo]

I researched this issue further. Taking the connection away from the pool when starting the bin log stream does not keep the pool invariants up to date. Furthermore, taking the connection away from the pool goes against the principle of using a pool (there is already a way to start a connection without a pool).

I wrote a method to close the binlog stream, along withtests (both with and without a pool -- in the case of a pool the test also checks that the pool can be disconnected). Please see #201

[blackbeam]

Superseded by #201
@oussama, sorry for delay and thanks for contribution.