ppc/pnv: Silence missing BMC warning with qtest

ppc/pnv: Silence missing BMC warning with qtest

The device introspect test in qtest emits some warnings with the
the pnv machine types during the "nodefaults" phase:

TEST check-qtest-ppc64: tests/qtest/device-introspect-test
qemu-system-ppc64: warning: machine has no BMC device. Use '-device
ipmi-bmc-sim,id=bmc0 -device isa-ipmi-bt,bmc=bmc0,irq=10' to define
one
qemu-system-ppc64: warning: machine has no BMC device. Use '-device
ipmi-bmc-sim,id=bmc0 -device isa-ipmi-bt,bmc=bmc0,irq=10' to define
one
qemu-system-ppc64: warning: machine has no BMC device. Use '-device
ipmi-bmc-sim,id=bmc0 -device isa-ipmi-bt,bmc=bmc0,irq=10' to define
one

This is expected since the pnv machine doesn't create the internal
BMC simulator fallback when "-nodefaults" is passed on the command
line, but these warnings appear in ci logs and confuse people.

Not having a BMC isn't recommended but it is still a supported
configuration, so a straightforward fix is to just silent this
warning when qtest is enabled.

Fixes: 25f3170b0654 ("ppc/pnv: Create BMC devices only when defaults are enabled")
Reported-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <159280903824.485572.831378159272329707.stgit@bahia.lan>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>