Apply CI labels on Nuxeo Server Docker Image

Currently the Nuxeo Server Docker image built by Jenkins X contains the labels below:

"Labels": {
    "org.label-schema.build-date": "20190801",
    "org.label-schema.license": "GPLv2",
    "org.label-schema.name": "CentOS Base Image",
    "org.label-schema.schema-version": "1.0",
    "org.label-schema.vendor": "CentOS"
}

They seem to be the ones from the CentOS image.

It doesn't seem possible to remove labels from inherited from the parent image, override is still possible.

According to the documentation we are encouraged to prefix our labels by a reverse DNS, such as org.nuxeo. With the values we have in CI, we're gonna label our docker image with:

• org.nuxeo.version: version of image being built
• org.nuxeo.scm-ref: the commit sha1
• org.nuxeo.build-tag: an unique tag representing which job has built the image

Note: The org.label-schema has been deprecated.