Add EXCLUDE_VERSIONS to explicitly set which versions not to build

[pkubatrh]

This is connected to #4 . As we are now pushing towards having the whole git history available in a single directory (be-it latest or the highest version available so far) to use git blame easily, we need to make sure we are able to both keep the Dockerfile.version history when a new version is introduced (which is most likely going to be the latest one) and to make the tests not fail in case centos/rhel packages are still not ready for the new version.

Currently to make sure the tests do not fail we would have to remove the Dockerfile.version specific to the distribution which does not yet have the packages available. This would however get rid of the git history of the Dockerfile we have been trying to preserve. This PR aims to fix this problem by introducing EXCLUDE_VERSIONS to common.mk and build.sh that can be used to explicitly provide information on which versions for which distribution to ignore.

@hhorak @torsava @praiskup WDYT

[pkubatrh]

I have also pushed this change to https://github.com/sclorg/container-common-scripts/tree/exclude_ver so that the CI can pickup the commit properly inside sclorg/postgresql-container#182

[hhorak]

Generally it makes sense to me, just a small comment about grep..

[hhorak]

I'm just thinking whether we can restrict the regexp a bit, since if we ever had something like such two files Dockerfile.fedora-module and Dockerfile.fedora in the repo, while having Dockerfile.fedora-module in EXCLUDE_VERSIONS, echo "${EXCLUDE_VERSIONS}" | grep ${dir}.${OS} would match both Dockerfile.fedora and Dockerfile.fedora-module..

grep -e "^\(.*\s\)\?${dir}.${OS}\(\s.*\)\?$" looks terrible though..

[pkubatrh]

Modified the change to not look at a make argument but instead check if a .exclude-$OS file is present in the versioned directory. If it exists, do not build the corresponding distribution version.

[praiskup]

lgtm

[praiskup]

As there's no other response, I'm merging. But even if there were future complaints -- with this one-liner implementation we can introduce other black-listing methods while keeping this one for compatibility reasons.