[Thinkit] Use absl::Cleanup to make sure thread is joined even if tes…

…t failed.[tests/flow] Only call `ClearTableEntries` when session is not null. Prolong traffic time for `VerifySamplingSizeWorks`.Use `BiglabStubCache` to generate a Testbed stub for `sflow_inband_test`. Enable punt test case.`ExtractTosFromTcpdumpResult` should return an error when ToS values are not the same. Verify ToS values are correctly set using tcpdump. (#885)



Co-authored-by: kishanps <kishanps@google.com>

tests/qos/packet_in_receiver.h

@@ -35,6 +35,7 @@ class PacketInReceiver final {
 
   // It's ok to call this function multiple times.
   void Destroy() {
+    session_.Finish();
     if (receiver_.joinable()) {
       stop_receiving_.Notify();
       receiver_.join();

tests/sflow/BUILD.bazel

@@ -41,6 +41,7 @@ cc_library(
         "//tests/lib:p4rt_fixed_table_programming_helper",
         "//tests/lib:switch_test_setup_helpers",
         "//tests/qos:gnmi_parsers",
+        "//tests/qos:packet_in_receiver",
         "//tests/qos:qos_test_util",
         "//thinkit:generic_testbed",
         "//thinkit:generic_testbed_fixture",
@@ -57,6 +58,7 @@ cc_library(
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/status:statusor",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/synchronization",
         "@com_google_absl//absl/time",
         "@com_google_absl//absl/types:span",
         "@com_google_googletest//:gtest",