logging: Move the logging test from OpenBSC into libosmocore

Add a testcase for the logging facility. The test is coming from
the OpenBSC code.
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 360f846..1cfae03 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -84,3 +84,10 @@
 cat $abs_srcdir/gsm0408/gsm0408_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/gsm0408/gsm0408_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([logging])
+AT_KEYWORDS([logging])
+cat $abs_srcdir/logging/logging_test.ok > expout
+cat $abs_srcdir/logging/logging_test.err > experr
+AT_CHECK([$abs_top_builddir/tests/logging/logging_test], [], [expout], [experr])
+AT_CLEANUP