Lower the report level of routine http errs in the Fog log

The FogLogger was automatically reporting every Excon error (400+ status
code) as an ERROR level message, which was then getting mirrored without
context into the evm.log as an ERROR.  The application already catches,
handles, and logs these occurances with relevant context, so the automatic
instrumentation only needs to report the gritty details of these events
at the DEBUG level.

lib/vmdb/loggers/fog_logger.rb

@@ -14,7 +14,7 @@ def instrument(name, params = {})
         case name
         when "excon.request" then  [:debug, message_for_excon_request(params)]
         when "excon.response" then [:debug, message_for_excon_response(params)]
-        when "excon.error" then    [:error, message_for_excon_error(params)]
+        when "excon.error" then    [:debug, message_for_excon_error(params)]
         else                   [:debug, message_for_other(params)]
         end