Add shared network for tempest testing

For some nova tests tempest creates instances without specifying
a network. As a result, neutron can't to create an interface on
external network (as in contrail env) or can't choose network if
we have several external or shared networks.

Change-Id: Id795300683ffe20a0a0b889b17401ba0629eaf91
Closes-bug: PROD-25148 (PROD:25148)
3 files changed