Activate systemd on SUSE distributions
Reduce redunancies in spec file

Remove redundant differences between SUSE and RHEL distributions.
Remove redundant mysql requirement

The mysql dependencies are recognized automatically during building.
Remove obsolete pgsqllib require on SUSE distributions
Use root as default user and group to prevent issues
Use permission verfication scripts on SUSE distributions
Prevent empty icinga2 package by adding COPYING

Empty packages are not allowed on SLES11 and also produce a warning in
newer openSUSE releases.

So we just work around the issue by adding the COPYING file.