sstables write: don't hide exception
sstables write: don't hide exception

Our sstable code currently has a bug (not solved by this patch) in writing
large summary files, where several aio write operations are done and one of
them fails with an EINVAL.

Unfortunately and inexplicably, sstable::write_simple simply *hides* this
exception (catches it and ignores it), so the write never knows it fails,
and we only get an exception later when sstable::write_components() tries
to load() the sstable it just created.

So in this patch, I remove the hiding of the exception, and now when writing
an sstable with 1,000,000 partitions, I see this in the output:

	failed to write sstable: Invalid argument

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@cloudius-systems.com>

duarten/scylla,glommer/scylla,capturePointer/scylla,gwicke/scylla,rluta/scylla,linearregression/scylla,phonkee/scylla,guiquanz/scylla,tempbottle/scylla,scylladb/scylla,gwicke/scylla,stamhe/scylla,scylladb/scylla,duarten/scylla,dwdm/scylla,justintung/scylla,linearregression/scylla,tempbottle/scylla,wildinto/scylla,eklitzke/scylla,avikivity/scylla,senseb/scylla,justintung/scylla,raphaelsc/scylla,rluta/scylla,wildinto/scylla,glommer/scylla,acbellini/scylla,kangkot/scylla,bowlofstew/scylla,glommer/scylla,rentongzhang/scylla,raphaelsc/scylla,asias/scylla,rentongzhang/scylla,kangkot/scylla,victorbriz/scylla,avikivity/scylla,bowlofstew/scylla,stamhe/scylla,gwicke/scylla,capturePointer/scylla,senseb/scylla,aruanruan/scylla,shaunstanislaus/scylla,eklitzke/scylla,dwdm/scylla,capturePointer/scylla,guiquanz/scylla,acbellini/scylla,kangkot/scylla,guiquanz/scylla,acbellini/scylla,victorbriz/scylla,asias/scylla,phonkee/scylla,justintung/scylla,tempbottle/scylla,respu/scylla,raphaelsc/scylla,linearregression/scylla,respu/scylla,eklitzke/scylla,stamhe/scylla,kjniemi/scylla,avikivity/scylla,wildinto/scylla,duarten/scylla,rluta/scylla,scylladb/scylla,phonkee/scylla,kjniemi/scylla,bowlofstew/scylla,kjniemi/scylla,aruanruan/scylla,shaunstanislaus/scylla,asias/scylla,respu/scylla,aruanruan/scylla,dwdm/scylla,rentongzhang/scylla,senseb/scylla,victorbriz/scylla,scylladb/scylla,shaunstanislaus/scylla