Create default network for more compute tests

Chipping away at the referenced bug, this commit uses the
create_default_network class-level variable introduced via [1] to
trigger setup_credentials to create a default network for another test
case in which the problem was observed.

[1] Ia34fe3b41261de02918713c2a948e6c56554bf6f
Partial-Bug: #1844568

Change-Id: Ic500aff5adda66328c292c936eaa097253360ea4
1 file changed