MINOR: systemd: report it when execve() fails

It's important to know that a signal sent to the wrapper had no effect
because something failed during execve(). Ideally more info (strerror)
should be reported. It would be nice to backport this to 1.6 and 1.5.
diff --git a/src/haproxy-systemd-wrapper.c b/src/haproxy-systemd-wrapper.c
index 15c48ca..f4fcab1 100644
--- a/src/haproxy-systemd-wrapper.c
+++ b/src/haproxy-systemd-wrapper.c
@@ -107,8 +107,12 @@
 		fprintf(stderr, "\n");
 
 		execv(argv[0], argv);
+		fprintf(stderr, SD_NOTICE "haproxy-systemd-wrapper: execv(%s) failed, please try again later.\n", argv[0]);
 		exit(1);
 	}
+	else if (pid == -1) {
+		fprintf(stderr, SD_NOTICE "haproxy-systemd-wrapper: failed to fork(), please try again later.\n");
+	}
 }
 
 static int read_pids(char ***pid_strv)
@@ -180,6 +184,7 @@
 	execv(wrapper_argv[0], wrapper_argv);
 	/* failed, let's reinstall the signal handler and continue */
 	setup_signal_handler();
+	fprintf(stderr, SD_NOTICE "haproxy-systemd-wrapper: re-exec(%s) failed.\n", wrapper_argv[0]);
 }
 
 /* handles SIGTERM and SIGINT only */