Silence the check-dirs check

The big shell fragment is just noise, for the common case where it
doesn't fail.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

Makefile.am

@@ -585,7 +585,7 @@ ganeti:
 
 .PHONY: check-dirs
 check-dirs: $(BUILT_SOURCES)
-	set -e; \
+	@set -e; \
 	find . -type d \( \( -name . \) -o \( \
 		-name .git -o \
 		-name autom4te.cache \