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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


"""Downloads file at url to the given path"""
    
    
    s = requests.Session()
    r = s.get(url, stream=True, verify=verify_ssl)
    total = 0
    try:
        if not os.path.exists(os.path.dirname(path)):
            os.makedirs(os.path.dirname(path))
        LOG.debug('Starting download from %s to %s (%s bytes)' % (url, path, r.headers.get('content-length')))
        with open(path, 'wb') as f:
            for chunk in r.iter_content(DOWNLOAD_CHUNK_SIZE):
                total += len(chunk)
                if chunk:  
                    f.write(chunk)
                    LOG.debug('Writing %s bytes (total %s) to %s' % (len(chunk), total, path))
                else:
                    LOG.debug('Empty chunk %s (total %s) from %s' % (chunk, total, url))
            f.flush()
            os.fsync(f)
    finally:
        LOG.debug('Done downloading %s, response code %s' % (url, r.status_code))
        r.close()
        s.close()
def parse_chunked_data(data):