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/.gitignore b/.gitignore
index 3dc916b..ac19b23 100644
--- a/.gitignore
+++ b/.gitignore
@@ -67,6 +67,7 @@
 tests/gsm0808/gsm0808_test
 tests/gb/bssgp_fc_test
 tests/gsm0408/gsm0408_test
+tests/logging/logging_test
 
 utils/osmo-arfcn
 utils/osmo-auc-gen