tests: check readability of cookie file

Author: ken2812221

test/functional/test_framework/util.py

@@ -326,7 +326,7 @@ def get_auth_cookie(datadir):
                 if line.startswith("rpcpassword="):
                     assert password is None  # Ensure that there is only one rpcpassword line
                     password = line.split("=")[1].strip("\n")
-    if os.path.isfile(os.path.join(datadir, "regtest", ".cookie")):
+    if os.path.isfile(os.path.join(datadir, "regtest", ".cookie")) and os.access(os.path.join(datadir, "regtest", ".cookie"), os.R_OK):
         with open(os.path.join(datadir, "regtest", ".cookie"), 'r', encoding="ascii") as f:
             userpass = f.read()
             split_userpass = userpass.split(':')