Add the possibility of starting multiple emulators at once

[ondracja]

Description:
For automated tests purposes, I'd like to have a possibility to work with 2 or more emulators at the same time in order to cover some edge cases like device switch test case.

Acceptance criteria:

1. It is possible to start multiple emulator instances of all types (2T1B1s, T1B1 + T2T1 etc.)
2. Programatically, I'm able to send signals to a specific device

[grdddj]

Need to discuss it with QA guys - what are the expectations, wanted interface, etc.

[grdddj]

Prerequisite is making node-bridge with the same API as old bridge @mroz22