Install yast2 to /usr/sbin like rest of package

This change also create backward compatible changes and
remove old deprecated compatible symlinks. It is needed to allow us use
common %configure in spec file and nothing special.
sbindir and sysconfdir: remove misplaced heuristic

It should be done as arguments to ./configure,
as done in previous commits.
sysconfdir: fixed also Makefile.cvs

Abolished the PREFIX variable: devtools/prefixbuild and similar tools
are removed in favor of VMs.
Merge pull request #115 from yast/sbin_to_usr

Install yast2 to /usr/sbin like rest of package
NetworkService: changed API to support more backends (namely wicked)

The change is backward incompatible
Updated changelog
NetworkService: Renamed cur_service_id_name -> current_name.

Also introduced accessor for current_name into public API to make
current_name read-only..

Renamed internal function get_net_service_name -> get_new_name
NetworkService: removed EnableDisable function

Reasons for removal:
- it worked for netconfig only
- it only Enabled the service
- it was replaced by more generic function EnableDisableNow
Code cleanup