Produce a more verbose output in cases when getpwnam() fails.

src/tarantool.m

@@ -775,8 +775,15 @@ main(int argc, char **argv)
 	if (cfg.username != NULL) {
 		if (getuid() == 0 || geteuid() == 0) {
 			struct passwd *pw;
+			errno = 0;
 			if ((pw = getpwnam(cfg.username)) == 0) {
-				say_syserror("getpwnam: %s", cfg.username);
+				if (errno) {
+					say_syserror("getpwnam: %s",
+						     cfg.username);
+				} else {
+					say_error("User not found: %s",
+						  cfg.username);
+				}
 				exit(EX_NOUSER);
 			}
 			if (setgid(pw->pw_gid) < 0 || setuid(pw->pw_uid) < 0 || seteuid(pw->pw_uid)) {