Adapt s390 IUCVTerminal to systemd

IUCVTerminal used to change inittab which doesn't exist anymore.

Instead of inittab the systemd getty templates "serial-getty@.service"
and "iucvtty@.service" are used.
"iucvtty@.service" is provided by s390-tools while
"serial-getty@.service" is provided by systemd.

Currently both templates need to be changed to work with my module but
the change for serial-getty was already accepted upstream so it should
most likely end up in SLES12 and the second is fixing a misleading name
of the iucvtty template for which I have already created a submit
request against s390-tools.

Additionally the terminal emulation selection was removed because it
isn't really needed.

While working on the module I have also replaced serveral unneeded Builtins
and Ops methods but left the rest of the code as it is.

If one of the two changes of our systemd templates doesn't get integrated for
for some reason I am going to update this module again but the current
approach is better than dealing with the terminal instances manually.