Enable SNI support for old python versions

[JelteF]

Summary:

We are thinking about using SNI for our certificates. This enables support for that on python versions lower than 2.7.9.

It also requires requests of at least version 2.4.1 for these python versions. This is because here the security extra is added that is used to pull in the SNI deps. These deps differ from requests release to requests release so they cannot be added manually easily.

Submitter checklist:

• [x] CHANGELOG updated or N/A
• [x] Documentation updated or N/A

Merger checklist:

• [x] ALL tests have passed
• [ ] Code Review is done
• [x] Dependencies satisfied