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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


if files:
        cleanup_tmp_files()
def cleanup_threads_and_processes(quiet=True):
    for t in TMP_THREADS:
        t.stop(quiet=quiet)
    for p in TMP_PROCESSES:
        try:
            p.terminate()
        except Exception as e:
            print(e)
    
    clear_list(TMP_THREADS)
    clear_list(TMP_PROCESSES)
def clear_list(l):
    while len(l):
        del l[0]
def cleanup_tmp_files():
    for tmp in TMP_FILES:
        try:
            rm_rf(tmp)
        except Exception:
            pass  
    del TMP_FILES[:]
def new_tmp_file():
    """ Return a path to a new temporary file. """
    tmp_file, tmp_path = tempfile.mkstemp()
    os.close(tmp_file)
    TMP_FILES.append(tmp_path)
    return tmp_path
def new_tmp_dir():