Trace when all log entries are deleted

It can be helpful for debug to know when someone deletes all of the
log entries at once, like when a user clicks the 'Delete all' button
on the web UI. If audit logs are ever implemented, it could be changed
to one of those instead.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I88b5c4a5e7830c64d3283de8f830f0cae4d501da
diff --git a/log_manager.hpp b/log_manager.hpp
index b8b250a..6dbd29c 100644
--- a/log_manager.hpp
+++ b/log_manager.hpp
@@ -371,6 +371,7 @@
      */
     void deleteAll() override
     {
+        log<level::INFO>("Deleting all log entries");
         manager.eraseAll();
     }