docker: make blockchain persistant

docker/docker-compose.yml

@@ -10,6 +10,7 @@ services:
         context: btcd/
       volumes:
             - shared:/rpc
+            - blockchain:/data
       environment:
         - RPCUSER
         - RPCPASS
@@ -59,3 +60,8 @@ volumes:
   # btcctl and lnd containers.
   shared:
     driver: local
+
+  # blockhain volume is needed for maintaining blockchain persistance
+  # during btcd container recreation.
+  blockchain:
+    driver: local