core: sat.conf is now first checked in /etc/_sat.conf for system-related settings

sat/core/constants.py

@@ -458,7 +458,10 @@ if (
         # per instance configurations (e.g. a dev instance and a main instance)
         root_dir = dirname(dirname(sat.__file__)) + '/'
         Const.CONFIG_PATHS = (
-            ["/etc/", "~/", "~/."]
+            # /etc/_sat.conf is used for system-related settings (e.g. when media_dir
+            # is set by the distribution and has not reason to change, or in a Docker
+            # image)
+            ["/etc/_", "/etc/", "~/", "~/."]
             + [
                 "%s/" % path
                 for path in list(BaseDirectory.load_config_paths(Const.APP_NAME_FILE))