replace hardcoded hostnames with environment variables

[vkuznet]

We have hardcoded host names, such as cmsweb.cern.ch, cmsweb-testbed.cern.ch in various places. For instance, these names are used in deploy scripts. But for k8s setup deploy scripts are used during build of image, i.e. it implies that these names are propagated into the image. We should remove all hardcoded host names and replace them as following:

cmsweb_prod=${CMSWEB_HOSTNAME:-cmsweb.cern.ch}
cmsweb_preprod=${CMSWEB_HOSTNAME:-cmsweb-testbed.cern.ch}

and then replace usage of host names with $cmsweb_prod and $cmsweb_preprod variables. This will allow to manipulate host names during k8s deployment where we can set appropriate host name via environment variables. Then we can adjust cmsweb docker images to rely on this environment variable.