add support for building swagger/OpenAPI JSON

to build, run `make swagger`; a file named `swagger.json` will be
written to the current working directory

Makefile

@@ -363,6 +363,12 @@ pyflakes: reports
 pylint: reports
 	@(set -o pipefail && $@ | reports/$@.report)
 
+swagger: reports
+	@if [ "$(VENV_BASE)" ]; then \
+		. $(VENV_BASE)/awx/bin/activate; \
+	fi; \
+	(set -o pipefail && py.test awx/main/tests/docs --release=$(RELEASE_VERSION) | tee reports/$@.report)
+
 check: flake8 pep8 # pyflakes pylint
 
 TEST_DIRS ?= awx/main/tests/unit awx/main/tests/functional awx/conf/tests awx/sso/tests