dac_start_destroy: Add cases for set_process_name as 1

When set_process_name as 1 in qemu conf, libvirt will have QEMU
set its process name to "qemu:VM_NAME", add test cases enable it
and check the qemu command.

Adjust set qemu.conf before per-VM seclabel, as seclabel will be
affected after qemu conf change.

Signed-off-by: Wayne Sun <gsun@redhat.com>