koji_builder: set use_bootstrap to false for new mock

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

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

@@ -5,6 +5,7 @@ config_opts['macros']['%bugurl'] = 'https://bugz.fedoraproject.org/%name'
 config_opts['nosync'] = True
 config_opts['nosync_force'] = True
 config_opts['environment']['LANG'] = 'C.UTF-8'
+config_opts['use_bootstrap'] = False
 {% if env == 'staging' %}
 if config_opts['chroot_name'].startswith('koji/epel8'):
    config_opts['dnf_common_opts'] = ['--setopt=module_platform_id=platform:el8']