standalone build fails

The build for standalone images doesn't work. Specifically:

Step 20/30 : ADD --chown=cmsinst:cmsinst siteconf/T3_CH_PublicCloud /cvmfs/cms.cern.ch/SITECONF/T3_CH_PublicCloud
ADD failed: file not found in build context or excluded by .dockerignore: stat siteconf/T3_CH_PublicCloud: file does not exist

siteconfig is now a dir up so it's missing from the perspective of the Dockerfile.