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>

test/test_reassembly.py

@@ -236,6 +236,8 @@ class TestIPv4Reassembly(TestIPReassemblyMixin, VppTestCase):
 
     def tearDown(self):
         super(TestIPv4Reassembly, self).tearDown()
+
+    def show_commands_at_teardown(self):
         self.logger.debug(self.vapi.ppcli("show ip4-reassembly details"))
         self.logger.debug(self.vapi.ppcli("show buffers"))
 
@@ -572,6 +574,8 @@ class TestIPv6Reassembly(TestIPReassemblyMixin, VppTestCase):
 
     def tearDown(self):
         super(TestIPv6Reassembly, self).tearDown()
+
+    def show_commands_at_teardown(self):
         self.logger.debug(self.vapi.ppcli("show ip6-reassembly details"))
         self.logger.debug(self.vapi.ppcli("show buffers"))
 
@@ -868,6 +872,8 @@ class TestIPv4ReassemblyLocalNode(VppTestCase):
 
     def tearDown(self):
         super(TestIPv4ReassemblyLocalNode, self).tearDown()
+
+    def show_commands_at_teardown(self):
         self.logger.debug(self.vapi.ppcli("show ip4-reassembly details"))
         self.logger.debug(self.vapi.ppcli("show buffers"))
 
@@ -1000,10 +1006,12 @@ class TestFIFReassembly(VppTestCase):
                                     expire_walk_interval_ms=10000, is_ip6=1)
 
     def tearDown(self):
+        super(TestFIFReassembly, self).tearDown()
+
+    def show_commands_at_teardown(self):
         self.logger.debug(self.vapi.ppcli("show ip4-reassembly details"))
         self.logger.debug(self.vapi.ppcli("show ip6-reassembly details"))
         self.logger.debug(self.vapi.ppcli("show buffers"))
-        super(TestFIFReassembly, self).tearDown()
 
     def verify_capture(self, capture, ip_class, dropped_packet_indexes=[]):
         """Verify captured packet stream.