Add ansible-base to requirements

Bumps minimum required Ansible to >= 2.10 as well.

The Ansible ecosystem has changed how their versions and packages work
causing the main `ansible` package versions to no longer determine the
version of `ansible-playbook`. Instead, the new `ansible-base` package
is what matters.

Background: https://blog.while-true-do.io/ansible-release-3-0-0/

For example, installing `ansible==2.10.7` would result in
`ansible-playbook==2.10.16` which was confusing.

By adding `ansible-base` to our `requirements.txt`, we'll get more
consistent and predictable version constraints.

Installing `ansible-base==2.10.16` would result in
`ansible-playbook==2.10.16` as you'd expect.

.circleci/config.yml

@@ -106,7 +106,7 @@ workflows:
           matrix:
             parameters:
               python-version: ["3.7.8", "2.7"]
-              ansible-version: ["~=2.9.0", "~=2.8.0"]
+              ansible-version: ["~=2.10.0"]
       - syntax-check-with-requirements-txt:
           name: syntax-check-python-<<matrix.python-version>>-requirements-txt
           matrix:

lib/trellis/plugins/vars/version.py

@@ -14,8 +14,8 @@
     from ansible.utils.display import Display
     display = Display()
 
-version_requirement = '2.8.0'
-version_tested_max = '2.10.7'
+version_requirement = '2.10.0'
+version_tested_max = '2.10.16'
 python3_required_version = '2.5.3'
 
 if version_info[0] == 3 and not ge(LooseVersion(__version__), LooseVersion(python3_required_version)):

requirements.txt

@@ -1,2 +1,3 @@
-ansible>=2.8.0,<3.0
+ansible>=2.10.0,<3.0
+ansible-base>=2.10,<=2.10.16
 passlib