Merge pull request jupyter-server#506 from candlerb/candlerb/extensio…

…n-backtrace

Include backtrace in debug output when extension fails to load

jupyter_server/extension/manager.py

@@ -1,4 +1,6 @@
 import importlib
+import sys
+import traceback
 
 from traitlets.config import LoggingConfigurable
 
@@ -339,6 +341,7 @@ def load_extension(self, name, serverapp):
                 extension.load_all_points(serverapp)
                 self.log.info("{name} | extension was successfully loaded.".format(name=name))
             except Exception as e:
+                self.log.debug("".join(traceback.format_exception(*sys.exc_info())))
                 self.log.warning("{name} | extension failed loading with message: {error}".format(name=name,error=str(e)))
 
     def link_all_extensions(self, serverapp):