IOSXR - get network instances

[Kani999]

Hello, I've created a very dirty "copy and paste" modification to iosxr driver which uses ios send_command methods for calling get_network_instances method provided by NAPALM.
Currently, this method is not implemented for IOSXR driver.

There is a "diff" example:
https://github.com/napalm-automation/napalm/compare/develop...Kani999:napalm:iosxr_get_network_instances?expand=1

I don't know if there is some plan to implement this method and if some part of this code could be used, but if somebody looks for a workaround you could use it.