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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


import psutil
        if not self.process:
            LOG.warning("No process found for command '%s'" % self.cmd)
            return
        parent_pid = self.process.pid
        try:
            parent = psutil.Process(parent_pid)
            for child in parent.children(recursive=True):
                child.kill()
            parent.kill()
            self.process = None
        except Exception:
            if not quiet:
                LOG.warning('Unable to kill process with pid %s' % parent_pid)
class JsonObject(object):
    """ Generic JSON serializable object for simplified subclassing """
    def to_json(self, indent=None):
        return json.dumps(self,
            default=lambda o: ((float(o) if o % 1 > 0 else int(o))
                if isinstance(o, decimal.Decimal) else o.__dict__),
            sort_keys=True, indent=indent)
    def apply_json(self, j):