alertmanager: update to 0.18.0

prometheus/alertmanager: upgrade to 0.17.0

prometheus: checkpath on log files

Update prometheus, alertmanager init scripts

Install prometheus data dir

Normalize alertmanager package

prometheus/prometheus: new APKBUILD

prometheus/alertmanager: new APKBUILD

Fix more indentation issues

Add py-prometheus-client

Add prometheus-node-exporter package