This removes use of gnutls and the TLS implementation, which is no
longer needed (task synchronization is handled via Taskchampion, which
uses `reqwest`, which handles TLS via other Rust dependencies). This
incidentally removes the following config options:
* `debug.tls`
* `taskd.ca`
* `taskd.certificate`
* `taskd.ciphers`
* `taskd.credentials`
* `taskd.key`
* `taskd.server`
* `taskd.trust`
This is an attempt at updating all docker configurations by simply
replacing the `python` packages with `python3`. The Travis CI will let
us know if this works.
These dockerfiles can be used to run taskwarrior's test suite on the
respective platforms using the following commands:
$ cd taskwarrior.git
$ docker build -t test-tw-fedora28 -f test/docker/fedora28 .
$ docker run test-tw-fedora28
For ubuntu, replace fedora28 with ubuntu1604.
