runsystest.py - automation script for system tests

Usage:
python runsystest.py --build 3.0.0-588 --params vbuckets=1024,xdcr_upr=false,upr=true --exclude inspect,install,rabbitmq,seriesly,worker,cluster,cbmonitor,systest,stats
--build  required param indicating which version-build the system test is to be run on
--params optional param to specify additional installer options
--exclude optional param to specify which steps to exclude

Change-Id: I993e0029e80571a4827908b3d4fc5d0cdc95bcbe
Reviewed-on: http://review.couchbase.org/35929
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>