Move ONAP pipelines to EST Tenant and enable keeping the stack

This change moves ONAP pipelines to City EST Tenant.

Apart from that, it introduces a new parameter, DELETE_STACK, so
the users of Jenkins can opt to keep the stack upon completion of
the job for troubleshooting purposes. Default is to delete the
stack.

No matter what, the stack will be deleted and recreated when the
same job gets triggered manually or on timer so the users need
to finish their jobs on the stack on time or they will be deleted.

Change-Id: I483c2b2723fae9a606342a38749f820dd9c7518d