tests: ensure build halts if tests fail during coverage mode

Makefile

@@ -47,6 +47,11 @@ COVER = for dir in $(GOLISTCOVER); do \
 			-covermode=count \
 			-coverprofile=$$dir/profile.tmp $$dir; \
 		\
+		if [ $$? != 0 ] ;\
+		then \
+		    exit 1 ;\
+		fi ;\
+		\
 		if [ -f $$dir/profile.tmp ]; then \
 			cat $$dir/profile.tmp | \
 				tail -n +2 >> profile.cov; \