build(Makefile): app ct should produce coverdata

Makefile

@@ -81,7 +81,7 @@ APPS=$(shell $(CURDIR)/scripts/find-apps.sh)
 .PHONY: $(APPS:%=%-ct)
 define gen-app-ct-target
 $1-ct: conf-segs
-	$(REBAR) ct --name $(CT_NODE_NAME) -v --suite $(shell $(CURDIR)/scripts/find-suites.sh $1)
+	@ENABLE_COVER_COMPILE=1 $(REBAR) ct --name $(CT_NODE_NAME) -c -v --suite $(shell $(CURDIR)/scripts/find-suites.sh $1)
 endef
 $(foreach app,$(APPS),$(eval $(call gen-app-ct-target,$(app))))