CBLT-198:  add script for job that sets defaults param values on other jobs.
This encapsulates the business logic in one script, and allows us to use a single
job to update other jobs, in case there are multiple builders all trying to update
the same job.

Change-Id: Ic2deaadefa2cef0ac078245a1c6b189cefb0e834
Reviewed-on: http://review.couchbase.org/34245
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>