Prepare support for a second BSC, in order to test OsmoBSCNAT.
* Rename BSC_* variables to BSC0_*
* Rename MGW4BSC_* variables to MGW4BSC0_*
* Rename osmo-bsc.cfg to osmo-bsc-0.cfg
* Rename osmo-mgw-for-bsc.cfg to osmo-mgw-for-bsc-0.cfg
Change-Id: Iaba2e3143b7bb6451a0104042e69d47ee5f48d3c