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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


' lambci/lambda:%s'
                ) % (docker_cmd, container_name, env_vars_str, network_str, runtime)
                LOG.debug(cmd)
                run(cmd)
                LOG.debug('Copying files to container "%s" from "%s".' % (container_name, lambda_cwd))
                cmd = (
                    '%s cp'
                    ' "%s/." "%s:/var/task"'
                ) % (docker_cmd, lambda_cwd, container_name)
                LOG.debug(cmd)
                run(cmd)
                LOG.debug('Starting container: %s' % container_name)
                cmd = '%s start %s' % (docker_cmd, container_name)
                LOG.debug(cmd)
                run(cmd)
                
                time.sleep(1)
            
            LOG.debug('Getting the entrypoint for image: lambci/lambda:%s' % runtime)
            cmd = (
                '%s image inspect'
                ' --format="{{ .ContainerConfig.Entrypoint }}"'
                ' lambci/lambda:%s'
            ) % (docker_cmd, runtime)
            LOG.debug(cmd)
            run_result = run(cmd)
            entry_point = run_result.strip('[]\n\r ')
            container_network = self.get_docker_container_network(func_arn)
            LOG.debug('Using entrypoint "%s" for container "%s" on network "%s".'
                % (entry_point, container_name, container_network))