gpg: use --batch for all invocations.

Suggested-by: docker-library/official-images#19467 (comment)

Author: thresheek

Dockerfile-debian.template

@@ -25,11 +25,11 @@ RUN set -x \
         pgp.mit.edu \
     ; do \
         echo "Fetching GPG key $NGINX_GPGKEY from $server"; \
-        gpg1 --keyserver "$server" --keyserver-options timeout=10 --recv-keys "$NGINX_GPGKEY" && found=yes && break; \
+        gpg1 --batch --keyserver "$server" --keyserver-options timeout=10 --recv-keys "$NGINX_GPGKEY" && found=yes && break; \
     done; \
     test -z "$found" && echo >&2 "error: failed to fetch GPG key $NGINX_GPGKEY" && exit 1; \
     done; \
-    gpg1 --export $NGINX_GPGKEYS > "$NGINX_GPGKEY_PATH" ; \
+    gpg1 --batch --export $NGINX_GPGKEYS > "$NGINX_GPGKEY_PATH" ; \
     rm -rf "$GNUPGHOME"; \
     apt-get remove --purge --auto-remove -y gnupg1 && rm -rf /var/lib/apt/lists/* \
     && dpkgArch="$(dpkg --print-architecture)" \