Fix proxy config

[CalvinNeo]

Signed-off-by: CalvinNeo calvinneo1995@gmail.com

What problem does this PR solve?

Issue Number: ref pingcap/tiflash#5170

Problem Summary:

1. gen_tikv_config is useless if we call TiKvConfig::from_file rather than make_tikv_config. We may turn to use address_proxy_config
2. ArgMatches in test can't process --config, so it shadows some errors.
3. We refactor some tests.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[breezewish]

the rest LGTM