chore(ephemeral): add debug log when bringing up ephemeral network (#…

…5010)

A debug message is logged whenever an instance is able to connect 
to the IMDS but when it can't, and an ephemeral network needs 
brought up, nothing is logged. Adding a log message here will help 
improve readability of logs and help troubleshoot failure paths 
when an instance is having issues with networking.

cloudinit/net/ephemeral.py

@@ -86,7 +86,12 @@ def __enter__(self):
                     self.connectivity_url_data["url"],
                 )
                 return
-
+            else:
+                LOG.debug(
+                    "Instance does not have connectivity to %s. Bringing up "
+                    "ephemeral network now.",
+                    self.connectivity_url_data["url"],
+                )
         try:
             self._bringup_device()