Handle html log annotations.

* modules/openstack_project/files/logstash/log-gearman-worker.py:
The annotated logs served by logs-dev and soon to be served to logs.o.o
return .txt files gzipped. log-gearman-worker.py needs to check the
Content-Type in the reponse headers to see if the txt files were gzipped
in order to properly handle this.

partial-bug: #1207047
Change-Id: I5981cde145a572a6e3d20e8369e407df151143ff
Merge "Handle html log annotations."