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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.request = request
        self.client_address = client_address
        self.server = server
        self.proxy = server.my_object
        self.data_bytes = None
        self.protocol_version = self.proxy.protocol_version
        try:
            BaseHTTPRequestHandler.__init__(self, request, client_address, server)
        except SSLError as e:
            LOG.warning('SSL error when handling request: %s' % e)
    def parse_request(self):
        result = BaseHTTPRequestHandler.parse_request(self)
        if not result:
            return result
        if sys.version_info[0] >= 3:
            return result
        
        
        expect = self.headers.get('Expect', '')
        if (expect.lower() == '100-continue' and
                self.protocol_version >= 'HTTP/1.1' and
                self.request_version >= 'HTTP/1.1'):
            if self.request_version != 'HTTP/0.9':
                self.wfile.write(('%s %d %s\r\n' %
                    (self.protocol_version, 100, 'Continue')).encode('latin1', 'strict'))
                self.end_headers()
        return result
    def do_GET(self):