Make sure log files are rotated

Currently, whilst deployed on PaaS the log files fill up until all
available space is used and then the app freezes.  This PR forces the
app to rotate log files every 10Mb with 5 backups.

This fixes #476

backdrop/core/log_handler.py

@@ -1,4 +1,5 @@
 from logging import FileHandler
+from logging.handlers import RotatingFileHandler
 from logstash_formatter import LogstashFormatter
 import logging
 from flask import request
@@ -18,15 +19,15 @@ def filter(self, record):
 
 
 def get_log_file_handler(path, log_level=logging.DEBUG):
-    handler = FileHandler(path)
+    handler = RotatingFileHandler(path, maxBytes=1024*1024*10, backupCount=5)
     handler.setFormatter(logging.Formatter(
         "%(asctime)s [%(levelname)s] -> %(message)s"))
     handler.setLevel(log_level)
     return handler
 
 
 def get_json_log_handler(path, app_name):
-    handler = FileHandler(path)
+    handler = RotatingFileHandler(path, maxBytes=1024*1024*10, backupCount=5)
     formatter = LogstashFormatter()
     formatter.defaults['@tags'] = ['application', app_name]
     handler.setFormatter(formatter)
@@ -64,19 +65,21 @@ def set_up_audit_logging(app, env):
 
 def create_request_logger(app):
     def log_request():
-        app.logger.info("request: %s - %s" % (request.method, request.url),
+        if request.method != "HEAD":
+            app.logger.info("request: %s - %s" % (request.method, request.url),
                         extra=create_logging_extra_dict())
     return log_request
 
 
 def create_response_logger(app):
     def log_response(response):
-        app.logger.info(
-            "response: %s - %s - %s" % (
-                request.method, request.url, response.status
-            ),
-            extra=create_logging_extra_dict()
-        )
+        if request.method != "HEAD":
+            app.logger.info(
+                "response: %s - %s - %s" % (
+                    request.method, request.url, response.status
+                ),
+                extra=create_logging_extra_dict()
+            )
         return response
     return log_response