Add javelin.log to logstash

Dependant on I787c08506d9a4d12081b5b5b16d752d5147f8e72 to collect the
javelin logs.

Since javelin2 uses tempest code to do the testing it generates useful
logs. As javelin2 grows to cover more we will most likely run into
issues that need debugging.
Add these logs to logstash to help us do analysis on javelin
results.

Change-Id: Ic3b2e33177bdc65fe294ddddd581a93de6c1cb60
Merge "Add javelin.log to logstash"