Feat: Usb-instance parameter to flash specific device

[F1rrel]

When multiple devices are connected and are in recovery mode, parameter --usb_instance allows to specify which one should be flashed. This allows to flash multiple devices in sequence using a script. How to find usb-instance.

Implemented changes:

• added parameter --usb_instance or -i
• changed _remove_identifier to also accept tuple in remove_list, which specifies number of identifiers to be removed (self-counted)
  • added --usb_instance and -i identifiers to be removed together with its value as it does not change the image
  • made global var IDENTIFIER_REMOVE_LIST to make it easier to reuse
• fixed paths to be inferred from script location instead of from where the script was run
• changed quit to return value based on success/error