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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 has_been_invoked_before:
            
            copy_command = '%s cp "%s/." "%s:/var/task";' % (docker_cmd, lambda_cwd, container_info.name)
        elif os.path.exists(event_file):
            
            copy_command = '%s cp "%s" "%s:/var/task";' % (docker_cmd, event_file, container_info.name)
        cmd = (
            '%s'
            ' %s exec'
            ' %s'  
            ' %s'  
            ' %s'  
        ) % (copy_command, docker_cmd, exec_env_vars, container_info.name, command)
        LOG.debug('Command for docker-reuse Lambda executor: %s' % cmd)
        return cmd
    def startup(self):
        self.cleanup()
        
        self.start_idle_container_destroyer_interval()
    def cleanup(self, arn=None):
        if arn:
            self.function_invoke_times.pop(arn, None)
            return self.destroy_docker_container(arn)
        self.function_invoke_times = {}
        return self.destroy_existing_docker_containers()
    def prime_docker_container(self, runtime, func_arn, env_vars, lambda_cwd):
        """
        Prepares a persistent docker container for a specific function.
        :param runtime: Lamda runtime environment. python2.7, nodejs6.10, etc.
        :param func_arn: The ARN of the lambda function.