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# Type of request: This is a bug report

# Detailed description
When running a java lambda in localstack with `LAMBDA_EXECUTOR=docker` and  `LAMBDA_JAVA_OPTS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=5005"` (replaced `_debug_port_` with `5005`), the port is not opened in the lambda execution docker container.

Looking at `Util.get_java_opts` in `localstack/services/awslambda/lambda_executors.py`, `debug_java_port` is not set in case `_debug_port_` is set

```
class Util:
    debug_java_port = False

    @classmethod
    def get_java_opts(cls):
        opts = config.LAMBDA_JAVA_OPTS or ''
        if '_debug_port_' in opts:
            if not cls.debug_java_port:
                cls.debug_java_port = get_free_tcp_port() ### <<< debug_java_port is only set here
            opts = opts.replace('_debug_port_', ('%s' % cls.debug_java_port))
        ### In other case, `cls.debug_java_port` is not set.
        return opts
```
## Expected behavior

`debug_java_port` should be set to the configured port

## Actual behavior

`debug_java_port` is empty

# Steps to reproduce
docker-compose file
```
version: '2.1'
services:
  localstack:
    container_name: localstack
    image: localstack/localstack
    privileged: true
    ports:
      - "4567-4582:4567-4582"
      - "9070:9070"
    environment:
      SERVICES: sqs,lambda
      DOCKER_HOST: unix:///var/run/docker.sock
      PORT_WEB_UI: 9070
      LAMBDA_EXECUTOR: docker
      LAMBDA_JAVA_OPTS: "-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=5005"
      DEBUG: 1
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - /tmp/localstack:/tmp/localstack
```

## Command used to start LocalStack

`docker-compose up`


import os
import re
import json
import unittest
import mock
import time
import datetime
from localstack.utils.common import save_file, new_tmp_dir, mkdir
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'