S allius/issue288 (#289)

* remove apostrophes from fmt strings

- thanks to @onkelenno for the suggestion

* improve the logger initializing

- don't overwrite the logging.ini settings if the
env variable LOG_LVL isn't well defined
- Thanks to @onkelenno for the idea to improve

* set default argument for LOG_LVL to INFO in docker files

* adapt unit test

ha_addons/ha_addon/Dockerfile

@@ -47,6 +47,8 @@ FROM base AS runtime
 
 ARG SERVICE_NAME
 ARG VERSION
+ARG LOG_LVL=INFO
+ENV LOG_LVL=$LOG_LVL
 ENV SERVICE_NAME=${SERVICE_NAME}