Activate systemd on SUSE distributions

refs #5818
Reduce redunancies in spec file

Remove redundant differences between SUSE and RHEL distributions.

refs #5818
Remove redundant mysql requirement

The mysql dependencies are recognized automatically during building.

refs #5818
Remove obsolete pgsqllib require on SUSE distributions

refs #5818
Use root as default user and group to prevent issues

refs #5818
Use permission verfication scripts on SUSE distributions

refs #5818
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.

refs #5818
Use Github url as tarball source

This allows the automatic download of new versions.

refs #5818
Remove redundant RPM Requires

refs #5818