Fix logs that interfere with JSON output by making warnings go to stderr instead of stdout (#602).

borgmatic/verbosity.py

@@ -1,7 +1,9 @@
 import logging
 
+import borgmatic.logger
+
 VERBOSITY_ERROR = -1
-VERBOSITY_WARNING = 0
+VERBOSITY_ANSWER = 0
 VERBOSITY_SOME = 1
 VERBOSITY_LOTS = 2
 
@@ -10,9 +12,11 @@ def verbosity_to_log_level(verbosity):
     '''
     Given a borgmatic verbosity value, return the corresponding Python log level.
     '''
+    borgmatic.logger.add_custom_log_levels()
+
     return {
         VERBOSITY_ERROR: logging.ERROR,
-        VERBOSITY_WARNING: logging.WARNING,
+        VERBOSITY_ANSWER: logging.ANSWER,
         VERBOSITY_SOME: logging.INFO,
         VERBOSITY_LOTS: logging.DEBUG,
     }.get(verbosity, logging.WARNING)