koji_builder / runroot: set nspawn args on runroot builders to get ostree_installer working

The ostree_installer job needs additional capabilities over the normal
mock systemd-spawn ones. So, add that here and since the
ostree_installer jobs are all runroot jobs we can isolate it to just the
runroot builders.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/koji_builder/templates/builders/site-defaults.cfg

@@ -8,3 +8,8 @@ config_opts['environment']['LANG'] = 'C.UTF-8'
 config_opts['use_bootstrap'] = True
 config_opts['yum_install_command'] += " -x devtoolset*"
 config_opts['dnf_warning'] = False
+{% if 'runroot' in group_names %}
+# We need to set this to get ostree_installer runroot jobs working
+# https://bugzilla.redhat.com/show_bug.cgi?id=2123812
+config_opts['nspawn_args'] += ['--capability=cap_mac_admin']
+{% endif %}