Fixes#7857.
* stop using urllib2 in test farm tests
* use six for urllib instead
* remove fabric lcd usage
* correct lcd removal
* remove fabric cd
* convert some remote calls to v2
* move more cxns to v2
* get run working with prefix
* get sudo commands working
* remove final fabric v1 references including local
* update requirements and README
* add new venv to gitignore
* update version used in travis
* remove deploy_script unused kwargs
* fix killboulder implementation so I can test creating a new boulder server
* hardcode the gopath due to broken env manamagement in fabric2
* Update letstest readme
* move the comment about hardcoding the ggopath
* catch BaseException instead of Exception
* work around fabric #2007
* use connections as context managers to ensure they're closed
* remove reference to virtualenv
I don't fully understand why, but since I updated my macbook to macOS Catalina, the test script currently fails to run for me with the versions of our dependencies we have pinned. Updating the dependencies solves the problem though and you can see Travis also successfully running tests with these new dependencies at https://travis-ci.com/certbot/certbot/builds/150573696.
