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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


return threading.currentThread().ident
    def stdout(self):
        return self._stdout.getvalue() if hasattr(self._stdout, 'getvalue') else self._stdout
    def stderr(self):
        return self._stderr.getvalue() if hasattr(self._stderr, 'getvalue') else self._stderr
def is_string(s, include_unicode=True):
    if isinstance(s, str):
        return True
    if include_unicode and isinstance(s, six.text_type):
        return True
    return False
def is_string_or_bytes(s):
    return is_string(s) or isinstance(s, six.string_types) or isinstance(s, bytes)
def md5(string):
    m = hashlib.md5()
    m.update(to_bytes(string))
    return m.hexdigest()
def in_docker():
    return config.in_docker()
def has_docker():
    try:
        run('docker ps')
        return True
    except Exception:
        return False
def is_port_open(port_or_url, http_path=None, expect_success=True):