sstables: Close _file even if random_access_reader::close() reports errors

close() operation is like a destructor, it cannot fail. It just
reports errors, but close itself succeeds. So we should proceed with
the closing even if it fails.
Message-Id: <1484245886-7269-1-git-send-email-tgrabiec@scylladb.com>

sstables/sstables.cc

@@ -132,7 +132,7 @@ public:
         seek(0);
     }
     virtual future<> close() override {
-        return random_access_reader::close().then([this] {
+        return random_access_reader::close().finally([this] {
             return _file.close().handle_exception([save = _file] (auto ep) {
                 sstlog.warn("sstable close failed: {}", ep);
                 general_disk_error();