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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


network = config.LAMBDA_DOCKER_NETWORK
        network_str = ' --network="%s" ' % network if network else ''
        docker_cmd = self._docker_cmd()
        if config.LAMBDA_REMOTE_DOCKER:
            cmd = (
                'CONTAINER_ID="$(%s create -i'
                ' %s'
                ' %s'
                ' %s'
                ' %s'  
                ' --rm'
                ' "lambci/lambda:%s" %s'
                ')";'
                '%s cp "%s/." "$CONTAINER_ID:/var/task"; '
                '%s start -ai "$CONTAINER_ID";'
            ) % (docker_cmd, entrypoint, debug_docker_java_port, env_vars_string, network_str, runtime, command,
                 docker_cmd, lambda_cwd,
                 docker_cmd)
        else:
            lambda_cwd_on_host = self.get_host_path_for_path_in_docker(lambda_cwd)
            cmd = (
                '%s run -i'
                ' %s -v "%s":/var/task'
                ' %s'
                ' %s'  
                ' --rm'
                ' "lambci/lambda:%s" %s'
            ) % (docker_cmd, entrypoint, lambda_cwd_on_host, env_vars_string, network_str, runtime, command)
        return cmd
    def get_host_path_for_path_in_docker(self, path):