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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


cert.set_issuer(cert.get_subject())
    cert.set_pubkey(k)
    cert.sign(k, 'sha1')
    cert_file = StringIO()
    key_file = StringIO()
    cert_file.write(to_str(crypto.dump_certificate(crypto.FILETYPE_PEM, cert)))
    key_file.write(to_str(crypto.dump_privatekey(crypto.FILETYPE_PEM, k)))
    cert_file_content = cert_file.getvalue().strip()
    key_file_content = key_file.getvalue().strip()
    file_content = '%s\n%s' % (key_file_content, cert_file_content)
    if target_file:
        save_file(target_file, file_content)
        key_file_name = '%s.key' % target_file
        cert_file_name = '%s.crt' % target_file
        save_file(key_file_name, key_file_content)
        save_file(cert_file_name, cert_file_content)
        TMP_FILES.append(target_file)
        TMP_FILES.append(key_file_name)
        TMP_FILES.append(cert_file_name)
        if random:
            return target_file, cert_file_name, key_file_name
        return file_content
    return file_content
def run_safe(_python_lambda, print_error=False, **kwargs):
    try:
        return _python_lambda(**kwargs)
    except Exception as e:
        if print_error:
            LOG.warning('Unable to execute function: %s' % e)
def run_cmd_safe(**kwargs):