daemon-helper: use _nm_strerror_r() to avoid non-thread-safe strerror()

Yes, there probably are not multiple threads here. It's a matter of principle to
not use smelly functions.

Also, copy the "errno" value we want to print, before calling various functions.

(cherry picked from commit c42f6f0997)
(cherry picked from commit 93359f2b32)

src/nm-daemon-helper/nm-daemon-helper.c

@@ -120,8 +120,8 @@ cmd_resolve_address(void)
                     service,
                     ret,
                     gai_strerror(ret),
-                    errno,
-                    strerror(errno));
+                    errsv,
+                    _nm_strerror_r(errsv, buf, sizeof(buf)));
         } else {
             fprintf(stderr,
                     "getnameinfo() via service '%s' failed: %d (%s)\n",