Add "RUN_ONLY_ONCE" option

.env.sample

@@ -9,6 +9,9 @@ DEBUG = "False"
 ## Debugging level, "info" is default, "debug" is more verbose
 DEBUG_LEVEL = "info"
 
+## If set to true then the script will only run once and then exit
+RUN_ONLY_ONCE = "False"
+
 ## How often to run the script in seconds
 SLEEP_DURATION = "3600"
 
@@ -27,7 +30,7 @@ LOGFILE = "log.log"
 ## Comma separated for multiple options
 #BLACKLIST_LIBRARY = ""
 #WHITELIST_LIBRARY = ""
-#BLACKLIST_LIBRARY_TYPE = "" 
+#BLACKLIST_LIBRARY_TYPE = ""
 #WHITELIST_LIBRARY_TYPE = ""
 #BLACKLIST_USERS = ""
 WHITELIST_USERS = "testuser1,testuser2"