Rename the test to virnetdaemontest and use virNetDaemon objects instead
of virNetServer inside.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

We were using "complicated" error printing in virnetservertest even
though we could've just dispatched the error.  Also add some good
practices that might come in handy (the code may fail without proper
initialization and event loop).
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

One string was already used only if that condition was true, second one
is added now.  Both are used in a nicer way.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

The virNetServer class has the ability to serialize its state
to a JSON file, and then re-load that data after an in-place
execve() call to re-connect to active file handles. This data
format is critical ABI that must have compatibility across
releases, so it should be tested...