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/mgcp/mgcp_test.ok b/openbsc/tests/mgcp/mgcp_test.ok
new file mode 100644
index 0000000..1a01c28
--- /dev/null
+++ b/openbsc/tests/mgcp/mgcp_test.ok
@@ -0,0 +1,2 @@
+Testing AUEP
+Done