Checkmk Werk 12820: mk_postgres: fixed user detection: use default user "postgres" in case of error

ID: 12820 Title: mk_postgres: fixed user detection: use default user "postgres" in case of error Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0i1 This werk fixes the user detection for postgresql docker images. If the user could no be determined the fallback user "postgres" is used.