CBQE-0: run_job_linux.sh: better handle parameterDefinitions

seems like in new jenkins version new params have been added for 'actions' key and the order of 'parameterDefinitions' changed
fix allows to skip first empty items in "actions", see http://qa.hq.northscale.net/job/debian_x64--01_02--XDCR_SSL-P0/api/python?pretty=true as example

Change-Id: I79d171a5579b6a13f8a7836633b4493bd2c1136f
Reviewed-on: http://review.couchbase.org/41999
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>