[branch-4.1][fix](regression) Avoid loopback HTTP TVF host

[hello-stephen]

What problem does this PR solve?

test_http_tvf starts an in-process HTTP server on the regression runner and asks Doris BE nodes to read from it. In branch-4.1 P2 build 203694, externalEnvIp is 127.0.0.1, so the case builds a URL such as http://127.0.0.1:46739/.... The remote BE interprets loopback as itself and fails with Connection refused.

What is changed?

Keep an explicit httpTvfHost override, but reject loopback/any-local values inherited from externalEnvIp and fall back to the runner host address.

TeamCity: http://172.20.48.17:8111/buildConfiguration/Doris_Doris_x64_branch41_Regression_P2/203694
Related backport: #65313

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[yiguolei]

run buildall

[hello-stephen]

p2 case , no need run

[hello-stephen]

skip buildall