Inject HOST_FQDN in var.env

Changes in this Pull Request:

Fix1: Substitute ${HOST_FQDN} in var.env (nested var.env variables cannot be resolved at runtime).

*Mandatory checks:**

[X] latest changes were fetched from the upstream branch before creating this PR (branch is up to date)
[ ] changes were tested manually
[ ] communication about interdependent changes has been sent to the team (if applicable)
[ ] respective Jenkins jobs were referenced in additional context section of this PR

OSCM Build References: TBD

This change is

servicecatalog / oscm-dockerbuild