Create default network for compute volume and negative metadata tests

server metadata and volume tests also create server without passing
the network to nova which further fail if more than one test network exists.

http://eavesdrop.openstack.org/irclogs/%23openstack-qa/%23openstack-qa.2020-03-03.log.html#t2020-03-03T15:57:34

Partial-Bug: #1844568
Change-Id: I9956946a4309b9a013fd53b0db06718372a9213c
10 files changed