Fix flaky conn tests that use time.time

[dpkp]

The time has come to fix these...

____________________________ test_connection_delay _____________________________
conn = <kafka.conn.BrokerConnection object at 0x0000000004cc50f8>
    def test_connection_delay(conn):
        conn.last_attempt = time.time()
>       assert round(conn.connection_delay()) == round(conn.config['reconnect_backoff_ms'])
E       assert 49.0 == 50.0
E        +  where 49.0 = round(49.48000907897949)
E        +    where 49.48000907897949 = <bound method BrokerConnection.connection_delay of <kafka.conn.BrokerConnection object at 0x0000000004cc50f8>>()
E        +      where <bound method BrokerConnection.connection_delay of <kafka.conn.BrokerConnection object at 0x0000000004cc50f8>> = <kafka.conn.BrokerConnection object at 0x0000000004cc50f8>.connection_delay
E        +  and   50.0 = round(50)
test/test_conn.py:84: AssertionError

---

This change is