test: Always start NetworkManager for NetworkCase tests
test: Always start NetworkManager for NetworkCase tests

Every now and then NetworkManager is not running and then bunch of tests fail.

Fixes #14877
Closes #14930
deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,garrett/cockpit,deryni/cockpit