scylla_raid_setup: check var-lib-scylla.mount existance before formatting RAID
scylla_raid_setup: check var-lib-scylla.mount existance before formatting RAID

We should run var-lib-scyllla.mount existance check before formatting RAID.

Fixes #6965

avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla