when the view is created from URL params, and sort is a string, the query fails

It naturally deals with complex expressions such as OR, AND, etc.
So there is no need to parse the string query anymore.
https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-simple-query-string-query.html

A list of values for a parameter is obtained with a URL
such as &param=value1&param=value2
The returned dictionary will be:
{ param : [value1, value2]}

The httplib module has been renamed to http.client in Python 3.
So let's try to import HTTPConnection from both.

- Fix errors:
  - TypeError: 'float' object cannot be interpreted as an integer

- Fix deprecation warnings:
  - DeprecationWarning: Please use assertEqual instead
  - DeprecationWarning: Please use assertTrue instead

[dependency] pin python-elasticsearch and python-elasticsearch-dsl versions as elasticsearch 7 has been released