Fix Huawei telnet ReadException: Unable to successfully split output based on pattern

[TimGa]

This PR fixes #2711

Root cause:

Unexpected nested group in regex pattern "combined_pattern".
For details please see: #2711 (comment).

Solution:

Change password_change_prompt regex group to non-capturing group. This change avoids nested group in combined_pattern, that solves the root cause. Actually nested group still presents in combined_pattern, but since this group is a non-capturing group, this solves the issue.

Side effects (not detected):

• Below in code, password_change_prompt used in re.search(password_change_prompt, output) statement. I've tested that changing group to non-capturing group do not affect the re.search statement.
• Suppose password_change_prompt will need to be passed inside the read_until_pattern method in future. In this case it also will not be a problem, because non-capturing group will be wrapped with parentheses which will change non-capturing group back to regular group, see line pattern = f"({pattern})":

                # The string matched by pattern must be retained in the output string.
                # re.split will do this if capturing parenthesis are used.
                if len(results) == 2:
                    # no capturing parenthesis, convert and try again.
                    pattern = f"({pattern})"
                    results = re.split(pattern, output, maxsplit=1, flags=re_flags)

• I've tested changes on about 1000 different huawei devices - it works good.

P.S. @ktbyers thank you for non-capturing group idea 👍