feat(es): make elasticsearch plugin work with python3

[nagypeterjob]

• [x] make it work on python3
• [x] add basic auth capability

[nagypeterjob]

I believe the python2.6 test suite breaks because of the Letsencrypt CA change: https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/

This should be a Travis side issue