fix fedora builds to not rely on python2-dnf and re-enable fedora builds

[joshrabinowitz]

Recent versions of fedora no longer include the package python2-dnf,
so the travis builds fail on fedora now.

See: ansible/ansible#54855

[joshrabinowitz]

We get the build-time error:

       failed: [localhost] (item=gawk) => { 
    ... "cmd": "dnf install -y python2-dnf",  
    ... "msg": "Error: Unable to find a match", ... 
     ]}

See: https://travis-ci.org/sobolevn/git-secret/jobs/544174411#L2586

[joshrabinowitz]

Not sure how to fix this one. @simbo1905 / @hurricanehrndz / @sobolevn ?

[sobolevn]

Some googling showed these results:

• https://bugzilla.redhat.com/show_bug.cgi?id=1696404
• python2-dnf used instead of python3-dnf (Fedora 30) ansible/ansible#54855

Maybe we can try to use python3 and python3-dnf?

[simbo1905]

Python 2 stops getting regular updates in 2020 so rhel8 and centos8 dont make it the default and instead folks need to choose between python2 or python3. Moving to python 3 seems sensible as its release date was 2008.

[joshrabinowitz]

@simbo1905, @sobolevn agreed, we need to move to a modern version of python.
Either of you up to perform this change?

[joshrabinowitz]

more details: Our build system (which uses python) has sort of been grandfathered in and we've been getting warnings in the builds about how we should move off python2 for some time now.

I'm hoping someone other than me is up to fixing this build issue as I'm mostly concentrated on the code in git-secret proper. Thanks in advance!

[joshrabinowitz]

See also: https://docs.ansible.com/ansible/latest/reference_appendices/python_3_support.html

[joshrabinowitz]

I think we're hitting neillturner/omnibus-ansible/issues/25 "Support for pip3" in omnibus-ansible, which is used by test-kitchen to install ansible with pip Nope, it's not that

[joshrabinowitz]

Fixed in #511 .

Edit: For reference, one of the steps needed was to get Ansible to prefer python3 if python2 was also installed using ansible_python_interpreter. See changes in #511 and https://docs.ansible.com/ansible/latest/reference_appendices/interpreter_discovery.html#interpreter-discovery