[Libguestfs] [PATCH nbdkit v2] tests: Rename and rework test-ipv4.sh so it tests

[Richard W.M. Jones]

This is my second go at reworking the ‘test-ipv4.sh’ test.

Instead of merely connecting to the server using socat, use
‘qemu-img info’ so that the test is slightly more realistic.

Also clean up old PID and log files before starting the test.

Previous version was posted here:
https://www.redhat.com/archives/libguestfs/2018-January/msg00253.html

Rich.