Hotfix for manila's jobs config

In jobs env var $BASE is used, it is empty for some reason
See next:
https://jenkins05.openstack.org/job/gate-manila-tempest-dsvm-neutron/99/console

Set this env var manually to be sure of correct job run.

Change-Id: I9af2972906e83ed7ed6a8f29f704042923779c91