automember: Fix behavior of unused parameters.

If a task with 'action: automember' tried to modify an automember rule
and did not provide either 'inclusive' or 'exclusive' parameters, the
regex for the missing arguments would be removed.

This patch fixes this behavior to only modify those parameters that
were set on the task, and leave the missing parameters in the state
they were before the task.

Tests have been updated to verify expected behavior.

Reference: https://bugzilla.redhat.com/show_bug.cgi?id=1976922