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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


x_forwarded_for = headers.get('X-Forwarded-For')
        client_address = self.client_address[0]
        server_address = ':'.join(map(str, self.server.server_address))
        if x_forwarded_for:
            x_forwarded_for_list = (x_forwarded_for, client_address, server_address)
        else:
            x_forwarded_for_list = (client_address, server_address)
        return ', '.join(x_forwarded_for_list)
    def forward(self, method):
        data = self.data_bytes
        forward_headers = CaseInsensitiveDict(self.headers)
        
        if forward_headers.get('Connection', '').lower() != 'keep-alive':
            self.close_connection = 1
        path = self.path
        if '://' in path:
            path = '/' + path.split('://', 1)[1].split('/', 1)[1]
        forward_url = self.proxy.forward_url
        for listener in self._listeners():
            if listener:
                forward_url = listener.get_forward_url(method, path, data, forward_headers) or forward_url