[bug#67613] Introduce unit tests for oci-container-service-type.

[paul]

Hi Ludo’ ,

I'm sending a patchset rebased on current master. I hope patch 1-3 are 
non-controversial enough to be directly merged as they add features 
without breaking existing configurations. About patch 4 and 5 I stand by 
my request for help in my last email.

Thank you for your work,


giacomo