Tests: Refactor tearDown show command logging, add lifecycle markers.

This change adds a consistent interface for adding test-specific show commands to
log.txt.

It also adds log markers for the execution of setUp[Class], tearDown[Class]
in the logs.

Change-Id: I7d42e396e594a59e866a7d55dac0af25548e657a
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/test_vxlan_gpe.py b/test/test_vxlan_gpe.py
index 36661a9..7ee1225 100644
--- a/test/test_vxlan_gpe.py
+++ b/test/test_vxlan_gpe.py
@@ -243,13 +243,14 @@
     #  @param self The object pointer.
     def tearDown(self):
         super(TestVxlanGpe, self).tearDown()
-        if not self.vpp_dead:
-            self.logger.info(self.vapi.cli("show bridge-domain 11 detail"))
-            self.logger.info(self.vapi.cli("show bridge-domain 12 detail"))
-            self.logger.info(self.vapi.cli("show bridge-domain 13 detail"))
-            self.logger.info(self.vapi.cli("show int"))
-            self.logger.info(self.vapi.cli("show vxlan-gpe"))
-            self.logger.info(self.vapi.cli("show trace"))
+
+    def show_commands_at_teardown(self):
+        self.logger.info(self.vapi.cli("show bridge-domain 11 detail"))
+        self.logger.info(self.vapi.cli("show bridge-domain 12 detail"))
+        self.logger.info(self.vapi.cli("show bridge-domain 13 detail"))
+        self.logger.info(self.vapi.cli("show int"))
+        self.logger.info(self.vapi.cli("show vxlan-gpe"))
+        self.logger.info(self.vapi.cli("show trace"))
 
 
 if __name__ == '__main__':