test: Print out qemu command when doing verbose testing

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
test: Work around for qemu 2.1.x bugs with powerdown

qemu 2.1.x has some bugs with powering off via ACPI, and qemu
not exiting when the VM halts. Add workaround for these for now.

https://bugzilla.redhat.com/show_bug.cgi?id=1139387
https://bugzilla.redhat.com/show_bug.cgi?id=1139357

Closes #1138
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>