Git short sha used for queue slices from end instead of beginning

[in03]

Git short shas are the first several digits, not the last.
Not essential, just good to keep consistent with the standard.

[in03]

Implemented in #165

Changed the slicing in all places where git SHAs are printed, e.g. for the new CLI banner build print. Now using a custom key for version constraint (queues, routing keys, etc), so this change has no implications on version constraining.