dist/common/scripts/scylla_raid_setup: skip constructing RAID0 when only one disk specified
dist/common/scripts/scylla_raid_setup: skip constructing RAID0 when only one disk specified

When only one disk specified, create XFS directly on the disk instead of
creating RAID0 volume on the disk.

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