Add onetime cli param

[sseide]

Patch to add new -onetime command line parameter to run the templateing process only once and exit afterwards.
This command line param overwrite the "Onetime" flag from all backend resources configured.

Issue related: #74

I have not found a place where to add this to the current documentation below the docs/ directory. Only mentioned flag inside the readme file instead.

Current patch is working as long as templates can be rendered - every is created and "remco" exits.

And another problem i found - current implementation does not respect the "onetime" config flag in case of an error (e.g. Network/Host unreachable, password wrong or templates not found etc.). Running into such a problem "remco" goes into an endless loop and retries again and again making the "Onetime" config param kinda useless.

I think remco should not go into a loop retrying when "ontime" flag is set for a specific config. What do you think?

[HeavyHorst]

I think remco should not go into a loop retrying when "ontime" flag is set for a specific config. What do you think?

Agreed. Could you create another pull request?