Not all customers want Container support in their Ínfix builds. This
patch adds build-time support for detecting if podman is enabled in
the configuration.
- Klish container commands have been broken out to their own xml file
- infix-interfaces have been given a 'containers' feature
- ietf-interfces.c enables 'containers' feature on an #ifdef
- infix-container.c is only built if --enable-containers
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>