Improve handling for true/false options in config file

Change-Id: I57cd3f82196ed841fb07c392bc4d6951f2fcd612
diff --git a/config/config.py b/config/config.py
index 02de5a8..e0c870f 100644
--- a/config/config.py
+++ b/config/config.py
@@ -32,9 +32,12 @@
 from errors import ConfigError
 
 def is_positive(text):
-    if text in ('1', 'y', 'Y', 't', 'T', 'True', 'true'):
+    valid_true = ('1', 'y', 'yes', 't', 'true')
+    valid_false = ('0', 'n', 'no', 'f', 'false')
+
+    if str(text) in valid_true or str(text).lower() in valid_true:
         return True
-    elif text in ('0', 'n', 'N', 'f', 'F', 'False', 'false'):
+    elif str(text) in valid_false or str(text).lower() in valid_false:
         return False
 
 def is_valid_logging_level(text):