tools: firmware: check for distro fallback udev cancel rule

Some distributions (Debian, OpenSUSE) have a udev rule in place to cancel
all fallback mechanism uevents immediately. This would obviously
make it hard to test against the fallback mechanism test interface,
so we need to check for this.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>