import oap_client_test from osmo-sgsn

As oap_client has moved from osmo-sgsn to libosmogsm, it is only fair
that the related unit test shall also be moved here.

Change-Id: I9d64e10b4bacac9b530cf077841bad762fc6d558
diff --git a/tests/oap/oap_client_test.ok b/tests/oap/oap_client_test.ok
new file mode 100644
index 0000000..59108a7
--- /dev/null
+++ b/tests/oap/oap_client_test.ok
@@ -0,0 +1,2 @@
+Testing OAP API
+Done