Fix use_host_resolv with new mock version (2017 Nov 22+)
    
    The change done in mock on 2017 Nov 22:
    
        782e150ffda41c55351c56eff6601a2cc1b8e4fe / [RHBZ#1514028]
    
    now requires rpmbuild_networking to be used together with use_host_resolv
    otherwise it does not have an affect. While setting up Fedora RISC-V koji
    instance we noticed that /etc/resolv.conf was never copied into chroot,
    while /ets/hosts was always present.
    
    The following was tested on Fedora RISC-V instance and resolved the original
    problem (buildSRPMFromSCM was failing on fedpkg sources as it couldn't
    resolve src.fedoraproject.org)
    
    Signed-off-by: David Abdurachmanov <david.abdurachmanov@gmail.com>