[#222] Add shard amount check

There should be at least one correctly set up shard in node config.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

cmd/neofs-node/config.go

@@ -449,6 +449,7 @@ func initShardOptions(c *cfg) {
 			configPath(writeCachePrefix, cfgBlobStorTreePath),
 		)
 		if useCache && writeCachePath == "" {
+			c.log.Warn("incorrect writeCache path, ignore shard")
 			break
 		}
 
@@ -458,6 +459,7 @@ func initShardOptions(c *cfg) {
 			configPath(blobPrefix, cfgBlobStorTreePath),
 		)
 		if blobPath == "" {
+			c.log.Warn("incorrect blobStor path, ignore shard")
 			break
 		}
 
@@ -545,6 +547,10 @@ func initShardOptions(c *cfg) {
 		)
 	}
 
+	if len(opts) == 0 {
+		fatalOnErr(errors.New("no correctly set up shards, exit"))
+	}
+
 	c.cfgObject.cfgLocalStorage.shardOpts = opts
 }