Item system.sw.os[name] returns "\S" in RHEL7 (and possibly in other systemd Linux distributions)

The file used by Zabbix to get the OS name, /etc/issue.net according to the documentation, has changed in RHEL7.

It seems that this information has moved to /etc/os-release (http://www.freedesktop.org/software/systemd/man/os-release.html) in distributions that use systemd.

I have attached two patches that fix this issue. It's probably not the best implementation, but you can use it if you're too busy to fix it anytime soon.