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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 os
import json
from flask import Flask, render_template, jsonify, send_from_directory, request
from flask_swagger import swagger
from localstack import config
from localstack.utils import common
from localstack.services import generic_proxy
from localstack.services import infra as services_infra
from localstack.constants import VERSION
from localstack.dashboard import infra
from localstack.utils.bootstrap import load_plugins, canonicalize_api_names
from localstack.utils.aws.aws_stack import Environment
root_path = os.path.dirname(os.path.realpath(__file__))
web_dir = root_path + '/web/'
app = Flask('app', template_folder=web_dir)
app.root_path = root_path
@app.route('/swagger.json')
def spec():
    swag = swagger(app)
    swag['info']['version'] = VERSION
    swag['info']['title'] = 'AWS Resources Dashboard'
    return jsonify(swag)
@app.route('/graph', methods=['POST'])
def get_graph():