rules: skip btrfs check if devices are not ready in 64-btrfs.rules (#8304)

rules: skip btrfs check if devices are not ready in 64-btrfs.rules (#8304)

If any devices are marked with 'SYSTEMD_READY=0' then we shouldn't run any
btrfs check on them.

Indeed there's no point in running "btrfs ready" on devices that already have
SYSTEMD_READY=0 set. Most probably such devices are members of a higher layer
aggregate device such as dm-multipath or software RAID. Doing IO on them wastes
time at best, and may cause delays, timeouts, or even hangs at worst (think
active-passive multipath or degraded RAID, for example).

It was initially reported at:
https://bugzilla.opensuse.org/show_bug.cgi?id=872929