Add initial OsmoBTS test suite

This Test suite implements the BSC-side of Abis RSL and is used to
test OsmoBTS.  It contains provisions for using L1CTL against
(virt_phy + osmo-bts-virtual) or (trxcon + fake_trx + osmo-bts-trx)
to also simulate the MS/Um side, bu those provisions are not used
yet.

Implemented tests currently are only related to RSL dedicated channel
activation / deactivation.

We still terminate OML inside OsmoBSC, and let the test suite deal
exclusively with RSL to keep complexity low.

Change-Id: I8ced0d29777aad3ec842d54eabea87dfcc943c79
diff --git a/Makefile b/Makefile
index 2fcc561..3f2230b 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-SUBDIRS=bsc bsc-nat ggsn_tests gprs_gb lapdm mgw msc selftest sgsn sysinfo
+SUBDIRS=bsc bsc-nat bts ggsn_tests gprs_gb lapdm mgw msc selftest sgsn sysinfo
 
 PARALLEL_MAKE:=-j4