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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 context:
            environment['AWS_LAMBDA_FUNCTION_NAME'] = context.function_name
            environment['AWS_LAMBDA_FUNCTION_VERSION'] = context.function_version
            environment['AWS_LAMBDA_FUNCTION_INVOKED_ARN'] = context.invoked_function_arn
        java_opts = Util.get_java_opts(self.debug_java_port)
        
        command = ''
        
        if runtime == LAMBDA_RUNTIME_JAVA8:
            stdin = None
            
            target_file = os.path.join(lambda_cwd, os.path.basename(LAMBDA_EXECUTOR_JAR))
            if not os.path.exists(target_file):
                cp_r(LAMBDA_EXECUTOR_JAR, target_file)
            
            taskdir = '/var/task'
            save_file(os.path.join(lambda_cwd, LAMBDA_EVENT_FILE), event_body)
            command = ("bash -c 'cd %s; java %s -cp \".:`ls *.jar | tr \"\\n\" \":\"`\" \"%s\" \"%s\" \"%s\"'" %
                (taskdir, java_opts, LAMBDA_EXECUTOR_CLASS, handler, LAMBDA_EVENT_FILE))
        
        cmd = self.prepare_execution(func_arn, environment, runtime, command, handler, lambda_cwd)
        
        LOG.debug('Running lambda cmd: %s' % cmd)
        result, log_output = self.run_lambda_executor(cmd, stdin, environment)
        log_formatted = log_output.strip().replace('\n', '\n> ')
        LOG.debug('Lambda %s result / log output:\n%s\n>%s' % (func_arn, result.strip(), log_formatted))
        return result, log_output
class LambdaExecutorReuseContainers(LambdaExecutorContainers):
    """ Executor class for executing Lambda functions in re-usable Docker containers """
    def __init__(self):