sstables: be more descriptive with filename parsing errors
sstables: be more descriptive with filename parsing errors

Currently, we don't let the user know even what is the filename that failed.
That information should be included in the message.

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@scylladb.com>

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