test: Robustify netcat invocation in TestCurrentMetrics.testNetwork
test: Robustify netcat invocation in TestCurrentMetrics.testNetwork

Disable DNS lookups for the server, which is sometimes unreliable and
not necessary.

Give nc a second to initialize, so that the client process can connect
more reliably.

Add verbosity to netcat, so that the logs tell us why the unit fails.

cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,garrett/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit