Use ansible_python to determine whether to use python3

The CentOS 8 / ansible_python_interpreter method is not reliable on
Debian when ansible_python_interpreter is not set.

Related: #24

Author: markgoddard

defaults/main.yml

@@ -64,6 +64,4 @@ libvirt_host_uri: >-
 
 # Whether the python3 version of the libvirt python bindings should be
 # installed. If false, the python 2 bindings will be installed.
-libvirt_host_python3: >-
-  {{ (ansible_os_family == 'RedHat' and ansible_distribution_major_version|int >= 8) or
-     ansible_python_interpreter | default('python') | basename is match('python3.*') }}
+libvirt_host_python3: "{{ ansible_python.version.major == 3 }}"