log/scripts: introduce proper log level fallback and env getter function (#2506)

This PR does two small things:

1. The log level, in case it is unset, will now be "calculated" from
   `/etc/dms-settings` and not always default to `info`. This way, we
   can ensure that more often than not, the log level the user chose
   when starting DMS is used everywhere.
2. I noticed that the way I obtained the log level could be used to
   obtain any env variable's log level. I therefore added a function to
   `utils.sh` in case we use it in the future.

target/scripts/helpers/utils.sh

@@ -11,3 +11,12 @@ function _is_comment
 {
   grep -q -E "^\s*$|^\s*#" <<< "${1}"
 }
+
+# Provide the name of an environment variable to this function
+# and it will return its value stored in /etc/dms-settings
+function _get_dms_env_value
+{
+  local VALUE
+  VALUE=$(grep "^${1}=" /etc/dms-settings | cut -d '=' -f 2)
+  printf '%s' "${VALUE:1:-1}"
+}