Handle log paths in logstash gearman client better

* modules/openstack_project/files/logstash/log-gearman-client.py:
Use os.path.join to join the base log path provided by Jenkins and the
log file provided in the gearman client config. This avoid needing to
worry about trailing slashes in the Jenkins provided path.

Change-Id: I973237dae6f0b7947d322489108a05a99a7cc0be
Merge "Handle log paths in logstash gearman client better"