main/nagios: fix ownership of installed files/directories

The ownership of most files/directories was set to the nagios user/group
which meant that they had write access to a lot more files that they
should have.

Upstream disables the ownership change in the makefiles[0] and does them
manually which I have ported to the APKBUILD.

[0]: https://github.com/NagiosEnterprises/nagioscore/blob/f6f417eff033f70301d4b19f3e424695b8017734/nagios.spec#L156