Reduce number of logs kept for merge and periodic jobs

Limit to max of 14 days or 10 total logs. Historical logs for these job
types aren't too useful and makes Jenkins WebUI take longer to load.
Let's reduce the amount of artifacts we keep for these types of jobs.

Change-Id: I4c3928ffaccc9231733c8369b3bc597866af3fec
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>