[UX-tool] Provide command line option to disable unification of app test and main console logs

After implementing the unification of app test and main console logs to improve the failure investigation on CI (https://github.com/dotnet/xharness/pull/1348), we realized that the same behavior might be unwanted in local environment. We should implement a command line option to disable the log merging behavior. Possibly as an option to `apple test` and `android test` commands.

We should decide if we want the unification of logs as a default or opt-in behavior.

fyi: @ivanpovazan