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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


if line in [None, '', b'']:
                                break
                            if not (line and line.strip()) and self.is_killed():
                                break
                            line = convert_line(line)
                            if filter_line(line):
                                continue
                            outstream.write(line)
                            outstream.flush()
                self.process.wait()
            else:
                self.process.communicate()
        except Exception as e:
            if self.process and not self.quiet:
                LOG.warning('Shell command error "%s": %s' % (e, self.cmd))
        if self.process and not self.quiet and self.process.returncode != 0:
            LOG.warning('Shell command exit code "%s": %s' % (self.process.returncode, self.cmd))
    def is_killed(self):
        if not self.process:
            return True
        if INFRA_STOPPED:
            return True
        
        
        
        import psutil
        return not psutil.pid_exists(self.process.pid)
    def stop(self, quiet=False):