install-deps.sh: do not enable unavailable repos

install-deps.sh: do not enable unavailable repos

should be specific when enabling codeready-builder repos, there is
chance that some repos are just not available, while the required one
is. for instance, "codeready-builder-for-rhel-8-x86_64-eus-debug-rpms"
might not be available. and in that case, `install-deps.sh` just fails.

so in this change, only the required one is enabled. see also
https://fedoraproject.org/wiki/EPEL

Signed-off-by: Kefu Chai <kchai@redhat.com>