dist/common/scripts/scylla_prepare: Change message to error
dist/common/scripts/scylla_prepare: Change message to error

Recently, Scylla was changed to mandate the use of XFS
for its data directories, unless the flag --developer-mode true
is provided. So during the AMI setup stage, if the user
did not provide extra disks for the setup scripts to prepare,
the scylla service will refuse to start. Therefore, the
message in scylla_prepare has to be changed to an actual
error message, and the file name, to be changed to
something that reflects the event that happened.

Signed-off-by: Lucas Meneghel Rodrigues <8ad3460456640ab580599f5440c5a8d925a620b9@scylladb.com>

duarten/scylla,kjniemi/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,raphaelsc/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla