Use pytest-custom_exit_code to pass when no tests are found

This is important for the directories where we don't yet have tests.
This is only relevant for when the Makefile runs pytest, because pants
only runs pytest on files that exist, but the Makefile
blindly tries to run on every component directory.

Makefile

@@ -77,7 +77,8 @@ endif
 # The minus in front of st2.st2common.bootstrap filters out logging statements from that module.
 # https://github.com/pytest-dev/pytest-xdist/issues/71
 #PYTEST_OPTS := -n auto --tx 2*popen//execmodel=eventlet
-PYTEST_OPTS := -s --log-level=error
+# --suppress-no-test-exit-code is part of the pytest-custom_exit_code plugin
+PYTEST_OPTS := -s --log-level=error --suppress-no-test-exit-code
 
 ifndef PIP_OPTIONS
 	PIP_OPTIONS :=
@@ -1099,7 +1100,7 @@ runners-itests: requirements .runners-itests
 		echo "==========================================================="; \
 		echo "Running integration tests in" $$component; \
 		echo "==========================================================="; \
-		. $(VIRTUALENV_DIR)/bin/activate; pytest --capture=no --verbose $(PYTEST_OPTS)
+		. $(VIRTUALENV_DIR)/bin/activate; pytest --capture=no --verbose $(PYTEST_OPTS) \
 			--cov=$$component --cov-report=html $$component/tests/integration || ((failed+=1)); \
 	done; \
 	echo failed=$$failed; \

test-requirements.txt

@@ -42,6 +42,8 @@ pytest-benchmark[histogram]==3.4.1
 pytest-icdiff==0.9
 pytest-cov==3.0.0
 pytest-xdist==2.5.0
+# for Makefile-based pytest runs
+pytest-custom_exit_code
 # zstandard is used for micro benchmarks
 zstandard==0.23.0
 # ujson is used for micro benchmarks