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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


mode = 'a' if append else 'w+'
    if not isinstance(content, six.string_types):
        mode = mode + 'b'
    with open(file, mode) as f:
        f.write(content)
        f.flush()
def load_file(file_path, default=None, mode=None):
    if not os.path.isfile(file_path):
        return default
    if not mode:
        mode = 'r'
    with open(file_path, mode) as f:
        result = f.read()
    return result
def to_str(obj, encoding=DEFAULT_ENCODING, errors='strict'):
    """ If ``obj`` is an instance of ``binary_type``, return
    ``obj.decode(encoding, errors)``, otherwise return ``obj`` """
    return obj.decode(encoding, errors) if isinstance(obj, six.binary_type) else obj
def to_bytes(obj, encoding=DEFAULT_ENCODING, errors='strict'):
    """ If ``obj`` is an instance of ``text_type``, return
    ``obj.encode(encoding, errors)``, otherwise return ``obj`` """
    return obj.encode(encoding, errors) if isinstance(obj, six.text_type) else obj
def cleanup(files=True, env=ENV_DEV, quiet=True):