Refactor RHEL publish

[JackPGreen]

The publish_rhel script is very long and although split out into functions, I found it difficult to reason exactly what it does.

Refactored by:

• updated tag_image_push_rhel to call the script directly rather than source-ing them and calling bits of them
• tidied up some repeated variables at the same time
• re-ordered function declarations by usage

This PR changes nothing else and doesn't fix anything, it's purely a refactor.

Example execution.

[nishaatr]

LGTM
Suggestion: could move Run preflight scan to the script as well or may be there is a reason why it was left out!

[JackPGreen]

LGTM Suggestion: could move Run preflight scan to the script as well or may be there is a reason why it was left out!

Don't really have a strong opinion either way, but having them as separate steps gives some external visibility on where were at in the job.

[nishaatr]

LGTM Suggestion: could move Run preflight scan to the script as well or may be there is a reason why it was left out!

Don't really have a strong opinion either way, but having them as separate steps gives some external visibility on where were at in the job.

No strong opinion from me also but thought make sense keeping RH interaction/logic nicely contained in one place. Don't believe this will affect visibility.
Additionally, may be we log functions with echo "starting to...". I see the wait functions are missing this perhaps because it does log little later. Another option is to group the logging then it will be more clearer

But not fussed with this!