stages/disks: reword condition
stages/disks: reword condition

This is just weird. The effect is the same, but this is much more
readable.

ajeddeloh/ignition,dgonyeo/ignition,coreos/ignition,higebu/ignition,higebu/ignition,higebu/ignition,AlexNPavel/ignition,dgonyeo/ignition,AlexNPavel/ignition,AlexNPavel/ignition,dgonyeo/ignition,coreos/ignition,ajeddeloh/ignition,coreos/ignition,ajeddeloh/ignition