Check with assertion as parameter throws "OSError: [Errno 98] Address already in use"

**Describe the bug**
When creating a check which accepts an assertion as a parameter, I get an error "OSError: [Errno 98] Address already in use"

**To Reproduce**
```
import sys
from pydeequ.analyzers import *
from pydeequ.checks import *
from pydeequ.verification import *
from pyspark.sql import SparkSession
from pyspark.sql.types import *

# data points to s3
# data = "s3://*****"

spark = SparkSession.builder.appName("pydeequ_poc").getOrCreate()
print("===== get spark context complete =====")
df = spark.read.parquet(data)
print("===== count: " + str(df.count()) + " =====")
df.printSchema()
verification_run_builder = VerificationSuite(spark).onData(df)
_check_name = "hasSize"
_assertion = "lambda x: x >= 3"
_args = [eval(_assertion)]
print("===== _args["+str(type(_args))+"]: " + str(_args) + " =====")
_check = Check(spark, CheckLevel.Warning, _check_name)
_check_func = getattr(_check, _check_name)
print("===== _check_func["+str(type(_check_func))+"]: " + str(_check_func) + " =====")
_check = _check_func(*_args)
print("===== _check["+str(type(_check))+"]: " + str(_check) + " =====")
verification_run_builder = verification_run_builder.addCheck(_check)
verification_result = verification_run_builder.run()
verification_result_df = verification_result.checkResultsAsDataFrame(spark, verification_result, pandas=False)
verification_result_df.show()
```

**Expected behavior**
Check is created, and results are generated.

**Log**
```
===== count: 2619203 =====
root
|-- marketplace: string (nullable = true)
|-- customer_id: string (nullable = true)
|-- review_id: string (nullable = true)
|-- product_id: string (nullable = true)
|-- product_parent: string (nullable = true)
|-- product_title: string (nullable = true)
|-- star_rating: integer (nullable = true)
|-- helpful_votes: integer (nullable = true)
|-- total_votes: integer (nullable = true)
|-- vine: string (nullable = true)
|-- verified_purchase: string (nullable = true)
|-- review_headline: string (nullable = true)
|-- review_body: string (nullable = true)
|-- review_date: date (nullable = true)
|-- year: integer (nullable = true)
|-- product_category: string (nullable = true)

===== _args[]: [ at 0xffffa15a2b90>] =====
===== _check_func[]: > =====
Traceback (most recent call last):
File "/usr/lib/spark/python/lib/py4j-0.10.9-src.zip/py4j/java_gateway.py", line 2207, in start
OSError: [Errno 98] Address already in use

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/opt/ammar/pydeequ_poc_pyspark.py", line 26, in
_check = _check_func(*_args)
File "/usr/local/lib/python3.7/site-packages/pydeequ/checks.py", line 134, in hasSize
assertion_func = ScalaFunction1(self._spark_session.sparkContext._gateway, assertion)
File "/usr/local/lib/python3.7/site-packages/pydeequ/scala_utils.py", line 32, in __init__
super().__init__(gateway)
File "/usr/local/lib/python3.7/site-packages/pydeequ/scala_utils.py", line 16, in __init__
self.gateway.start_callback_server()
File "/usr/lib/spark/python/lib/py4j-0.10.9-src.zip/py4j/java_gateway.py", line 1894, in start_callback_server
File "/usr/lib/spark/python/lib/py4j-0.10.9-src.zip/py4j/java_gateway.py", line 2216, in start
py4j.protocol.Py4JNetworkError: An error occurred while trying to start the callback server (127.0.0.1:25334)
21/11/19 13:44:06 INFO SparkContext: Invoking stop() from shutdown hook
```

**Additional context**
I am submitting the spark job using LIVY from an airflow task. Spark has default configs.

Start with pydeequ/checks.py at hasSize and scala_utils.py at ScalaFunction1, then reproduce the callback-server startup through the Livy/Airflow Spark context described in the issue. Check how Py4J starts the server and verify that an assertion-based check can be created and run without the address-in-use error, producing verification results.

Scritto dal modello di indicizzazione a partire dal testo della issue.