Better comment in logstash job submission role

Be more explicit in the logstash job submissions role library code about
why we can get away with treating foo.txt and foo.txt.gz as the same
content.

Change-Id: I44a7310f7aa149919cc9aa38510329ce879c8f17

roles/submit-log-processor-jobs/library/submit_log_processor_jobs.py

@@ -40,6 +40,10 @@ class File(object):
     def __init__(self, name, tags):
         # Note that even if we upload a .gz we want to use the logical
         # non compressed name for handling (it is easier on humans).
+        # The reason we can get away with this is that this name is used
+        # to construct the log_url below. The server serving that
+        # log_url treats foo.txt and foo.txt.gz as being the same content
+        # and serves both paths from the same backend content.
         if name.endswith('.gz'):
             self._name = name[:-3]
         else: