When the storage_service::restore_tablets() resolves, it only means that
tablet transitions are done, including restore transitions, but not
necessarily that they succeeded. So before resolving the restoration
task with success need to check if all sstables were downloaded and, if
not, resolve the task with exception.
Test included. It uses fault-injection to abort downloading of a single
sstable early, then checks that the error was properly propagated back
to the task waiting API
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Move the download_sstable and get_sstables_for_tablet static functions
from sstables_loader into a new file to make them reusable by the
tablet-aware restore code.
