CB-7978 Fixed launching chrome in Linux

- Fixed launching chrome in linux. It either launches chrome or google-chrome processes
- Reads config.xml looking for the source file to be used at the lauching of the browser. This will work for Linux, Windows and MacOs
You are right, something I didn't notice at that time. The `google-chrome` process is detached, so if the user wants to keep using Cordova CLI for other tasks he can do it, but this is not the same as for `chrome` process.
Moreover, the other platforms (Mac and Windows) don't have a handler like the one in Linux I'm proposing. My question to you is, should I get rid of the `unref` and let the child process block the parent (and hence the user won't be able to use the CLI until he/she closes chrome) or unify the behavior for other platforms as well? Keep in mind that the change will affect other platforms, not just Linux as in this PR