tests: Introduce running tests with GNU autotest in OpenBSC

The quality of the tests is of different value but it is good to
get started and improve from here.
diff --git a/openbsc/tests/channel/Makefile.am b/openbsc/tests/channel/Makefile.am
index 404ab32..4f50dab 100644
--- a/openbsc/tests/channel/Makefile.am
+++ b/openbsc/tests/channel/Makefile.am
@@ -1,6 +1,8 @@
 INCLUDES = $(all_includes) -I$(top_srcdir)/include
 AM_CFLAGS=-Wall -ggdb3 $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS)
 
+EXTRA_DIST = channel_test.ok
+
 noinst_PROGRAMS = channel_test
 
 channel_test_SOURCES = channel_test.c
diff --git a/openbsc/tests/channel/channel_test.ok b/openbsc/tests/channel/channel_test.ok
new file mode 100644
index 0000000..7976aee
--- /dev/null
+++ b/openbsc/tests/channel/channel_test.ok
@@ -0,0 +1,2 @@
+Testing the gsm_subscriber chan logic
+Reached, didn't crash, test passed