CBQE-0: add runlist support to --fromfile option

for launching ad-hoc runlists
python cbsystest.py run test --cluster default --fromfile tests/runlist.js

Change-Id: I3e6072785d2395206286e4de21c508111f2efece
Reviewed-on: http://review.couchbase.org/26158
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>