<!-- Love localstack? Please consider supporting our collective:
👉  https://opencollective.com/localstack/donate -->
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 unittest
import json
from localstack.services.awslambda import lambda_api, lambda_executors
from localstack.utils.aws.aws_models import LambdaFunction
class TestLambdaAPI(unittest.TestCase):
    CODE_SIZE = 50
    CODE_SHA_256 = '/u60ZpAA9bzZPVwb8d4390i5oqP1YAObUwV03CZvsWA='
    MEMORY_SIZE = 128
    ROLE = 'arn:aws:iam::123456:role/role-name'
    LAST_MODIFIED = '2019-05-25T17:00:48.260+0000'
    TRACING_CONFIG = {'Mode': 'PassThrough'}
    REVISION_ID = 'e54dbcf8-e3ef-44ab-9af7-8dbef510608a'
    HANDLER = 'index.handler'
    RUNTIME = 'node.js4.3'
    TIMEOUT = 60  
    FUNCTION_NAME = 'test1'
    ALIAS_NAME = 'alias1'
    ALIAS2_NAME = 'alias2'
    RESOURCENOTFOUND_EXCEPTION = 'ResourceNotFoundException'
    RESOURCENOTFOUND_MESSAGE = 'Function not found: %s'
    ALIASEXISTS_EXCEPTION = 'ResourceConflictException'
    ALIASEXISTS_MESSAGE = 'Alias already exists: %s'