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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


self.client.put('/2017-10-31/functions/{0}/concurrency'.format(self.FUNCTION_NAME),
                            data=json.dumps(concurrency_data))
            response = self.client.get('{0}/functions/{1}'.format(lambda_api.PATH_ROOT, self.FUNCTION_NAME))
            result = json.loads(response.get_data())
            self.assertTrue('Concurrency' in result)
            self.assertDictEqual(concurrency_data, result['Concurrency'])
    def test_list_tags(self):
        with self.app.test_request_context():
            self._create_function(self.FUNCTION_NAME, self.TAGS)
            arn = lambda_api.func_arn(self.FUNCTION_NAME)
            response = self.client.get('{0}/tags/{1}'.format(lambda_api.PATH_ROOT, arn))
            result = json.loads(response.get_data())
            self.assertTrue('Tags' in result)
            self.assertDictEqual(self.TAGS, result['Tags'])
    def test_tag_resource(self):
        with self.app.test_request_context():
            self._create_function(self.FUNCTION_NAME)
            arn = lambda_api.func_arn(self.FUNCTION_NAME)
            response = self.client.get('{0}/tags/{1}'.format(lambda_api.PATH_ROOT, arn))
            result = json.loads(response.get_data())
            self.assertTrue('Tags' in result)
            self.assertDictEqual({}, result['Tags'])
            self.client.post('{0}/tags/{1}'.format(lambda_api.PATH_ROOT, arn), data=json.dumps({'Tags': self.TAGS}))
            response = self.client.get('{0}/tags/{1}'.format(lambda_api.PATH_ROOT, arn))
            result = json.loads(response.get_data())
            self.assertTrue('Tags' in result)
            self.assertDictEqual(self.TAGS, result['Tags'])
    def test_tag_non_existent_function_returns_error(self):
        with self.app.test_request_context():
            arn = lambda_api.func_arn('non-existent-function')