Use regular OS when using slim container image

Context

• Follow-up of !729 (comment 1564861331)
• Pre-requisite of !729 (merged)

What does this MR do and why?

Fetch chrome OS packages for slim distributions.

If using a slim OS, we still want to get the regular OS chrome packages.

Reproduce locally

slim version

bash

OS_VERSION=bullseyeE2_a_bit-longer123-slim
if [[ $OS_VERSION =~ .+-slim ]]; then
    OS_VERSION=${OS_VERSION%%-slim}
fi

$ echo "${OS_VERSION}"
bullseyeE2_a_bit-longer123

non-slim version

bash

OS_VERSION=bullseyeE2_a_bit-longer123-nonslim
if [[ $OS_VERSION =~ .+-slim ]]; then
    OS_VERSION=${OS_VERSION%%-slim}
fi

$ echo "${OS_VERSION}"
bullseyeE2_a_bit-longer123-nonslim

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.