When starting bitcoind, create/load default wallet as needed

Since Bitcoin Core will no longer do so; see
bitcoin/bitcoin#15454

Tested with all of the following bitcoind versions:

0.17.1
0.19.0.1
0.20.1
0.18.0
0.20.0
v0.21.0rc1 (from git)

glacierscript.py

@@ -307,11 +307,38 @@ def ensure_bitcoind_running():
     while times <= 20:
         times += 1
         if bitcoin_cli_call("getnetworkinfo") == 0:
+            create_default_wallet()
             return
         time.sleep(0.5)
 
     raise Exception("Timeout while starting bitcoin server")
 
+
+def create_default_wallet():
+    """
+    Ensure the default wallet exists and is loaded.
+
+    Since v0.21, Bitcoin Core will not create a default wallet when
+    started for the first time.
+    """
+    loaded_wallets = bitcoin_cli_json("listwallets")
+    if "" in loaded_wallets:
+        return  # default wallet already loaded
+    all_wallets = bitcoin_cli_json("listwalletdir")
+    # {
+    #     "wallets": [
+    #         {
+    #             "name": ""
+    #         }
+    #     ]
+    # }
+    found = any(w["name"] == "" for w in all_wallets["wallets"])
+    cmd = "loadwallet" if found else "createwallet"
+    loaded_wallet = bitcoin_cli_json(cmd, "")
+    if len(loaded_wallet["warning"]):
+        raise Exception("problem running {} on default wallet".format(cmd))  # pragma: no cover
+
+
 def require_minimum_bitcoind_version(min_version):
     """
     Fail if the bitcoind version in use is older than required