Create Gambia Jobs for Yardstick 1/2

Add Gambia jobs for Yardstick gate:
- yardstick-verify-gambia
- yardstick-merge-gambia
Keep fraser jobs until Gambia 7.0.0 is released.

Gambia jobs for Yardstick daily will be added in next patch.

Change-Id: Id02bcb8197dd1f6d0b8f5baddef684a97e269a14
Signed-off-by: jenkins-ci <jenkins-opnfv-ci@opnfv.org>
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>
Signed-off-by: rexlee8776 <limingjiang@huawei.com>
Signed-off-by: Patrice Buriez <patrice.buriez@intel.com>