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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


ALIASNOTFOUND_EXCEPTION = 'ResourceNotFoundException'
    ALIASNOTFOUND_MESSAGE = 'Alias not found: %s'
    TEST_UUID = 'Test'
    TAGS = {'hello': 'world', 'env': 'prod'}
    def setUp(self):
        lambda_api.cleanup()
        self.maxDiff = None
        self.app = lambda_api.app
        self.app.testing = True
        self.client = self.app.test_client()
    def test_get_non_existent_function_returns_error(self):
        with self.app.test_request_context():
            result = json.loads(lambda_api.get_function('non_existent_function_name').get_data())
            self.assertEqual(self.RESOURCENOTFOUND_EXCEPTION, result['__type'])
            self.assertEqual(
                self.RESOURCENOTFOUND_MESSAGE % lambda_api.func_arn('non_existent_function_name'),
                result['message'])
    def test_get_event_source_mapping(self):
        with self.app.test_request_context():
            lambda_api.event_source_mappings.append({'UUID': self.TEST_UUID})
            result = lambda_api.get_event_source_mapping(self.TEST_UUID)
            self.assertEqual(json.loads(result.get_data()).get('UUID'), self.TEST_UUID)
    def test_delete_event_source_mapping(self):
        with self.app.test_request_context():
            lambda_api.event_source_mappings.append({'UUID': self.TEST_UUID})
            result = lambda_api.delete_event_source_mapping(self.TEST_UUID)
            self.assertEqual(json.loads(result.get_data()).get('UUID'), self.TEST_UUID)
            self.assertEqual(0, len(lambda_api.event_source_mappings))
    def test_create_event_source_mapping(self):
        self.client.post('{0}/event-source-mappings/'.format(lambda_api.PATH_ROOT),