Merge #14788: tests: Possible fix the permission error when the tests open the cookie file

d6b3790 tests: check readability of cookie file (Chun Kuan Lee)

Pull request description:

  This PR would wait until the `.cookie` file is readable
  Possible fix no. 5 `PermissionError` in #14446

Tree-SHA512: e7055c7ca26a6eadbbe19e4eef08ffee61cd17de79b30af2f0d090f0ad81ca24815e3c7e034e5e30d47c580bb0b221b3955e9ff2fcec2274fbf7b9232ab0cdc7

Author: MarcoFalke

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(':')