Support DEBIAN_TIMESTAMP environment variables

Author: xumia

scripts/build_mirror_config.sh

@@ -24,7 +24,7 @@ if [ "$MIRROR_SNAPSHOT" == y ]; then
     if [ -f $MIRROR_VERSION_FILE ]; then
         DEBIAN_TIMESTAMP=$(grep "^debian==" $MIRROR_VERSION_FILE | tail -n 1 | sed 's/.*==//')
         DEBIAN_SECURITY_TIMESTAMP=$(grep "^debian-security==" $MIRROR_VERSION_FILE | tail -n 1 | sed 's/.*==//')
-    else
+    elif [ -z "$DEBIAN_TIMESTAMP" ] || [ -z "$DEBIAN_SECURITY_TIMESTAMP" ]; then
         DEBIAN_TIMESTAMP=$(curl $DEFAULT_MIRROR_URL_PREFIX/snapshot/debian/latest/timestamp)
         DEBIAN_SECURITY_TIMESTAMP=$(curl $DEFAULT_MIRROR_URL_PREFIX/snapshot/debian-security/latest/timestamp)
     fi