CBQE-0: run_job_linux.sh with group

currently the script ignores group for the tests
it is a continuation of changes
https://github.com/couchbase/testrunner/commit/9e55d8659ca792d616231f3fe8c554f1455c8d22
now if group is not set in any job then by default all tests will be run: GROUP=ALL

Change-Id: I59b00e19a366b96b61bfeb63d0d82042b8e7fae2
Reviewed-on: http://review.couchbase.org/39282
Reviewed-by: Aruna Piravi <aruna@couchbase.com>
Tested-by: buildbot <build@couchbase.com>