Check for rpcuser/rpcpassword first then for cookie

Better to check that rpcuser and rpcpassword exist then to check for
the cookie in the test framework.

Name an argument for consistency in p2p-segwit.py

test/functional/p2p-segwit.py

@@ -1944,7 +1944,7 @@ class SegWitTest(BitcoinTestFramework):
         self.test_signature_version_1()
         self.test_non_standard_witness()
         sync_blocks(self.nodes)
-        self.test_upgrade_after_activation(2)
+        self.test_upgrade_after_activation(node_id=2)
         self.test_witness_sigops()
 
 

test/functional/test_framework/util.py

@@ -192,15 +192,10 @@ def get_datadir_path(dirname, n):
     return os.path.join(dirname, "node"+str(n))
 
 def get_auth_cookie(datadir, n):
-    if os.path.isfile(os.path.join(datadir, "regtest", ".cookie")):
-        with open(os.path.join(datadir, "regtest", ".cookie"), 'r') as f:
-            userpass = f.read()
-            split_userpass = userpass.split(':')
-            return split_userpass[0], split_userpass[1]
-    else:
-        with open(os.path.join(datadir, "bitcoin.conf"), 'r') as f:
     user = None
     password = None
+    if os.path.isfile(os.path.join(datadir, "bitcoin.conf")):
+        with open(os.path.join(datadir, "bitcoin.conf"), 'r') as f:
             for line in f:
                 if line.startswith("rpcuser="):
                     assert user is None # Ensure that there is only one rpcuser line
@@ -208,7 +203,13 @@ def get_auth_cookie(datadir, n):
                 if line.startswith("rpcpassword="):
                     assert password is None # Ensure that there is only one rpcpassword line
                     password = line.split("=")[1].strip("\n")
-            if user is None and password is None:
+    if os.path.isfile(os.path.join(datadir, "regtest", ".cookie")):
+        with open(os.path.join(datadir, "regtest", ".cookie"), 'r') as f:
+            userpass = f.read()
+            split_userpass = userpass.split(':')
+            user = split_userpass[0]
+            password = split_userpass[1]
+    if user is None or password is None:
         raise ValueError("No RPC credentials")
     return user, password