base: On rhel8 machines set /usr/bin/python to /usr/bin/python3

The reason we do this is so we can use a few scripts (like nag-once)
as python2 on python2 hosts and python3 on rhel8 hosts.
Note that this depends on the script working on either.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/base/tasks/main.yml

@@ -525,3 +525,16 @@
   - base
   - config
   - krb5
+
+# rhel8 hosts do not have /usr/bin/python, but there are a few things we call 
+# with that because they also run the same on python2 hosts. 
+# So, we set python3 to /usr/bin/python on those hosts:
+- name: set /usr/bin/python to python3 on rhel8 hosts
+  alternatives:
+    name: python
+    link: /usr/bin/python
+    path: /usr/bin/python3
+  tags:
+  - base
+  - config
+  - python3alternative