testing: set and use REPORT_TO_BUILD_COP_BOT (#3822)

fixes #3821

This PR needs an internal Kokoro config change.

Author: Takashi Matsuo

.kokoro/python2.7/periodic.cfg

@@ -19,3 +19,8 @@ env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-docs-samples/.kokoro/tests/run_tests.sh"
 }
+
+env_vars: {
+    key: "REPORT_TO_BUILD_COP_BOT"
+    value: "True"
+}

.kokoro/python3.6/periodic.cfg

@@ -19,3 +19,8 @@ env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-docs-samples/.kokoro/tests/run_tests.sh"
 }
+
+env_vars: {
+    key: "REPORT_TO_BUILD_COP_BOT"
+    value: "True"
+}

.kokoro/python3.7/periodic.cfg

@@ -19,3 +19,8 @@ env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-docs-samples/.kokoro/tests/run_tests.sh"
 }
+
+env_vars: {
+    key: "REPORT_TO_BUILD_COP_BOT"
+    value: "True"
+}

.kokoro/python3.8/periodic.cfg

@@ -19,3 +19,8 @@ env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-docs-samples/.kokoro/tests/run_tests.sh"
 }
+
+env_vars: {
+    key: "REPORT_TO_BUILD_COP_BOT"
+    value: "True"
+}

.kokoro/tests/run_tests.sh

@@ -104,9 +104,11 @@ for file in **/requirements.txt; do
     nox -s "$RUN_TESTS_SESSION"
     EXIT=$?
 
-    # If this is a periodic build, send the test log to the Build Cop Bot.
-    # See https://github.com/googleapis/repo-automation-bots/tree/master/packages/buildcop.
-    if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"periodic"* ]]; then
+    # If REPORT_TO_BUILD_COP_BOT is set to "True", send the test log
+    # to the Build Cop Bot.
+    # See:
+    # https://github.com/googleapis/repo-automation-bots/tree/master/packages/buildcop.
+    if [[ "${REPORT_TO_BUILD_COP_BOT:-}" == "True" ]]; then
       chmod +x $KOKORO_GFILE_DIR/linux_amd64/buildcop
       $KOKORO_GFILE_DIR/linux_amd64/buildcop
     fi