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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


:param env_vars: The environment variables for the lambda.
        :param lambda_cwd: The local directory containing the code for the lambda function.
        :return: ContainerInfo class containing the container name and default entry point.
        """
        with self.docker_container_lock:
            
            container_name = self.get_container_name(func_arn)
            docker_cmd = self._docker_cmd()
            status = self.get_docker_container_status(func_arn)
            LOG.debug('Priming docker container (status "%s"): %s' % (status, container_name))
            
            if status < 1:
                
                self.destroy_docker_container(func_arn)
                env_vars_str = ' '.join(['-e {}={}'.format(k, cmd_quote(v)) for (k, v) in env_vars])
                network = config.LAMBDA_DOCKER_NETWORK
                network_str = ' --network="%s" ' % network if network else ''
                
                LOG.debug('Creating container: %s' % container_name)
                cmd = (
                    '%s create'
                    ' --rm'
                    ' --name "%s"'
                    ' --entrypoint /bin/bash'  
                    ' --interactive'  
                    ' -e AWS_LAMBDA_EVENT_BODY="$AWS_LAMBDA_EVENT_BODY"'
                    ' -e HOSTNAME="$HOSTNAME"'
                    ' -e LOCALSTACK_HOSTNAME="$LOCALSTACK_HOSTNAME"'
                    '  %s'  
                    '  %s'