Arcyd: refactor, for clarity 'repo' -> 'repo_name'

There's pretty much one usage of the word 'repo' that means
'repository name' instead of git repository callable.  Rename it to
'repo_name' instead for clarity.

Test Plan:
$ ./precommit.sh
Arcyd: re-use repo callables between cycles

Enable the possibility of caching git info between cycles by re-using
the git callable objects between cycles.

Hoist the creation of the abdt_git.Repo up to abdi_processrepolist and
persist the repo by adding it as a parameter to the functools.partial
call.

Test Plan:
$ ./precommit.sh