UrfArbitrator: really don't fail if /dev/rfkill isn't available.

Signed-off-by: Mathieu Trudel-Lapierre <mathieu.trudel-lapierre@canonical.com>
profiles: add a QEMU profile where key_control is disabled by default

QEMU devices don't necessarily have obvious key control devices
available from udev; avoid failing to start urfkill there just because
the input controls don't start.

Signed-off-by: Mathieu Trudel-Lapierre <mathieu.trudel-lapierre@canonical.com>