Allow specifying url(s) for interactive browsers tests

[hillin]

💡 Feature description

wasm-pack test now hosts interactive browsers tests at http://127.0.0.1:8000. It would be great if this url can be configured with an argument. In our case we'd like to run some tests on a mobile device connected to the intranet.

💻 Basic example

wasm-pack test --chrome --urls=http://0.0.0.0:8000