Do not run tempest run if the custom params are placeholders

Stop starting the tempest run in the offline workspace in
case the tempest_custom.yaml file has placeholders because the
preparation script is not executed.

Related-PROD: PROD-37187
Change-Id: I2eb44279424d3cc98b334ba63a73a6af63359880
(cherry picked from commit f6bc7b34a4faf5d4c6506ffd2419ab10c5aa571e)
2 files changed