Remove unused and commented rewrite rule
Try a syntax using jinja template and Salt pillar to dynamically set reverse proxy target:
  * use rproxy_target pillar for target
  * use rproxy_target_header to set the 'Host' HTTP header
Specify jinja template for nginx.conf
Move everything that is common to all minion, no matter their role from relay/ to minion-common/ (probes are technically not considered as relay but still need common elements)
Set default file to empty for rproxy_target.sls (shall contain association between minion ID and nginx rev. proxy target)