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We have several Kinesis streams set up with event notifications that trigger lambdas.  When the LAMBDA_EXECUTOR is set to 'docker' and we send a large number or records to Kinesis, multiple Lambdas will execute, but currently they are failing to create with error:

```
Exception: Lambda process returned error status code: 1. Output:
time="2019-09-18T17:28:11Z" level=error msg="error getting events from daemon: net/http: request canceled" 
Error response from daemon: driver failed programming external connectivity on endpoint busy_sanderson (a78e45a41d0ce5b0d8bab6ff54344fc34fe2b4969f55bf568e753121abc8759e): Bind for 0.0.0.0:38763 failed: port is already allocated
```

I believe this is due to the new debug_java_port introduced with this PR https://github.com/localstack/localstack/pull/1523

With this change, you are setting the port in the constructor by using a method known to have a race condition (https://github.com/localstack/localstack/blob/master/localstack/utils/common.py#L354)
(https://gist.github.com/gabrielfalcao/20e567e188f588b65ba2)

This should be changed to ensure unique ports are being issued across all lambdas


if not is_port_open(port, http_path=http_path, expect_success=expect_success):
            raise Exception()
    return retry(check, sleep=sleep_time, retries=retries)
def get_free_tcp_port():
    tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    tcp.bind(('', 0))
    addr, port = tcp.getsockname()
    tcp.close()
    return port
def get_service_protocol():
    return 'https' if config.USE_SSL else 'http'
def timestamp(time=None, format=TIMESTAMP_FORMAT):
    if not time:
        time = datetime.utcnow()
    if isinstance(time, six.integer_types + (float, )):
        time = datetime.fromtimestamp(time)
    return time.strftime(format)
def retry(function, retries=3, sleep=1, sleep_before=0, **kwargs):
    raise_error = None
    if sleep_before > 0:
        time.sleep(sleep_before)
    for i in range(0, retries + 1):
        try:
            return function(**kwargs)
        except Exception as error:
            raise_error = error
            time.sleep(sleep)
    raise raise_error
def dump_thread_info():