virt: Warn if uid==0 and nettype==user

Sample output:

15:37:08 INFO | Starting test ...
15:37:08 DEBUG| Test parameters:
                     ...
15:39:52 WARNI|
15:39:52 WARNI| Testing with nettype='user' while running as root may
                produce unexpected results!!!
15:39:52 WARNI|
Signed-off-by: NChris Evich <cevich@redhat.com>