Only run coverage on merges/pushes to master (#1783)

Makefile

@@ -80,6 +80,10 @@ integrations: build
 
 .PHONY: test
 test:
+	go test $(PACKAGES)
+
+.PHONY: test-coverage
+test-coverage:
 	for PKG in $(PACKAGES); do go test -cover -coverprofile $$GOPATH/src/$$PKG/coverage.out $$PKG || exit 1; done;
 
 .PHONY: test-vendor