[BUG] pool.close fails when callback is provided; causing memory leak

[larstbone]

In function pool.close(), if a callback is provided, the subsequent loop on "freeConnections" does nothing because that structure was previously zeroed out earlier in the function. The foreach should be performed on the local const "connections" which was a copy of "freeConnections" before being zeroed out.

The tests do not catch this because they validate that "freeConnections" is zero afterwards, which it is. But because of the bug, the actual connections were not closed.

The code block that runs when callback is provided

NOW
async.each(this.freeConnections, (connection, cb) => {
connection.nativeClose((error) => {
this.poolSize--;
cb(error);
});
}, error => callback(error));

SHOULD BE
async.each(connections, (connection, cb) => {
connection.nativeClose((error) => {
this.poolSize--;
cb(error);
});
}, error => callback(error));