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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


expected = '-Xmx512M'
        result = self.prepareJavaOpts(expected)
        self.assertEqual(expected, result)
    def test_java_options_with_memory_options_and_agentlib_option(self):
        expected = '-Xmx512M -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=10000'
        result = self.prepareJavaOpts('-Xmx512M -agentlib:jdwp=transport=dt_socket,server=y'
                                      ',suspend=y,address=_debug_port_')
        self.assertEqual(expected, result)
    def prepareJavaOpts(self, java_opts):
        lambda_executors.config.LAMBDA_JAVA_OPTS = java_opts
        result = lambda_executors.Util.get_java_opts(10000)
        return result
    def _create_function(self, function_name, tags={}):
        arn = lambda_api.func_arn(function_name)
        lambda_api.arn_to_lambda[arn] = LambdaFunction(arn)
        lambda_api.arn_to_lambda[arn].versions = {
            '$LATEST': {'CodeSize': self.CODE_SIZE, 'CodeSha256': self.CODE_SHA_256, 'RevisionId': self.REVISION_ID}
        }
        lambda_api.arn_to_lambda[arn].handler = self.HANDLER
        lambda_api.arn_to_lambda[arn].runtime = self.RUNTIME
        lambda_api.arn_to_lambda[arn].timeout = self.TIMEOUT
        lambda_api.arn_to_lambda[arn].tags = tags
        lambda_api.arn_to_lambda[arn].envvars = {}
        lambda_api.arn_to_lambda[arn].last_modified = self.LAST_MODIFIED
        lambda_api.arn_to_lambda[arn].role = self.ROLE
        lambda_api.arn_to_lambda[arn].memory_size = self.MEMORY_SIZE