Adds discovery rule, to limit discovery of IS-IS Status neighbors to specific subnets

[rvmack]

• adds "IS-IS Neighbor discovery" in Network section of checkmk's service discovery rules
  • can limit discovery of IS-IS neighbors to specific subnets
  • can add service labels during discovery

[curtisbowden]

Thanks @rvmack, I will review in the next day or so

[curtisbowden]

@rvmack I tested your wato plugin on cmk-raw-v2.1 since cmk-raw-v2.2 was failing with an internal server error.

I've merged your pull-request and added isis_adjacency_params.py to package so it will be included in the .mkp file in the release.