[rpmbuild] enforce use_host_resolv

Fixes: fedora-copr#747, PR#748
Related: rhbz#1676596
Related: rpm-software-management/mock#260

rpmbuild/make_srpm_mock.cfg

@@ -1,5 +1,6 @@
 include('/etc/mock/default.cfg')
 config_opts['rpmbuild_networking'] = True
+config_opts['use_host_resolv'] = True
 config_opts['chroot_additional_packages'] = 'make dnf'
 config_opts['plugin_conf']['bind_mount_enable'] = True
 config_opts['nspawn_args'] = ['--private-users=pick','--drop-capability=CAP_SYS_ADMIN,CAP_IPC_OWNER,CAP_KILL,CAP_LEASE,CAP_LINUX_IMMUTABLE,CAP_NET_BIND_SERVICE,CAP_NET_BROADCAST,CAP_NET_RAW,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT,CAP_SYS_NICE,CAP_SYS_PTRACE,CAP_SYS_TTY_CONFIG,CAP_SYS_RESOURCE,CAP_SYS_BOOT,CAP_AUDIT_WRITE,CAP_AUDIT_CONTROL']