Allow rpmbuild as non-root user

[nichivo]

Installing with user and group permissions here requires root access which shouldn't be required for building an RPM. It also assumes a "sogo" user and group exists.

This change shouldn't affect the final file permissions after installing the RPM as the permissions are set in the %files section on line 332:

%config(noreplace) %attr(0640, root, %sogo_user) %{_sysconfdir}/sogo/sogo.conf

[bbbenjie]

This important PR is still open aside that the CLA was not signed yet. @cgx, how do you rate the code changes? It prevents me from building a SOGo package as a non-root user.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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