tests: Add [+-]feature and feature=on|off test cases

Add test code to ensure features are enabled/disabled correctly in the
command-line. The test case use the "feature-words" and
"filtered-features" properties to check if the features were
enabled/disabled correctly.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170508183205.10884-1-ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
