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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`


LAMBDA_EXECUTOR_JAR = INSTALL_PATH_LOCALSTACK_FAT_JAR
LAMBDA_EXECUTOR_CLASS = 'cloud.localstack.LambdaExecutor'
EVENT_FILE_PATTERN = '%s/lambda.event.*.json' % config.TMP_FOLDER
LAMBDA_RUNTIME_PYTHON27 = 'python2.7'
LAMBDA_RUNTIME_PYTHON36 = 'python3.6'
LAMBDA_RUNTIME_PYTHON37 = 'python3.7'
LAMBDA_RUNTIME_PYTHON38 = 'python3.8'
LAMBDA_RUNTIME_NODEJS = 'nodejs'
LAMBDA_RUNTIME_NODEJS43 = 'nodejs4.3'
LAMBDA_RUNTIME_NODEJS610 = 'nodejs6.10'
LAMBDA_RUNTIME_NODEJS810 = 'nodejs8.10'
LAMBDA_RUNTIME_NODEJS10X = 'nodejs10.x'
LAMBDA_RUNTIME_NODEJS12X = 'nodejs12.x'
LAMBDA_RUNTIME_JAVA8 = 'java8'
LAMBDA_RUNTIME_JAVA11 = 'java11'
LAMBDA_RUNTIME_DOTNETCORE2 = 'dotnetcore2.0'
LAMBDA_RUNTIME_DOTNETCORE21 = 'dotnetcore2.1'
LAMBDA_RUNTIME_GOLANG = 'go1.x'
LAMBDA_RUNTIME_RUBY = 'ruby'
LAMBDA_RUNTIME_RUBY25 = 'ruby2.5'
LAMBDA_RUNTIME_PROVIDED = 'provided'
LAMBDA_EVENT_FILE = 'event_file.json'
LAMBDA_SERVER_UNIQUE_PORTS = 500
LAMBDA_SERVER_PORT_OFFSET = 5000
LAMBDA_API_UNIQUE_PORTS = 500
LAMBDA_API_PORT_OFFSET = 9000
LOG = logging.getLogger(__name__)
MAX_CONTAINER_IDLE_TIME_MS = 600 * 1000
EVENT_SOURCE_SQS = 'aws:sqs'
def get_from_event(event, key):