Change argument handling in `remote-test-server` and add new flags
This PR updates `remote-test-server` to add two new flags:
* `--sequential` disables parallel test execution, accepting one connection at the time instead. We need this for Ferrocene as one of our emulators occasionally deadlocks when running multiple tests in parallel.
* `--bind <ip:port>` allows customizing the IP and port `remote-test-server` binds to, rather than using the default value.
While I was changing the flags, and [after chatting on what to do on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/326414-t-infra.2Fbootstrap/topic/remote-test-server.20flags), I took this opportunity to cleanup argument handling in `remote-test-server`, which is a breaking change:
* The `verbose` argument has been renamed to the `--verbose` flag.
* The `remote` argument has been removed in favor of the `--bind 0.0.0.0:12345` flag. The only thing the argument did was to change the bound IP to 0.0.0.0, which can easily be replicated with `--bind` and also is not secure as our "remote" default.
I'm also open to keep the old arguments with deprecation warnings.
r? `@Mark-Simulacrum`
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