Arcyd: inject git object into processrepo

So that we can gradually replace direct dependence on phlsys_git with an
abstraction; inject the required git object into process repo instead of
just the path.

Take the opportunity to consolidate some of the test code in
abdi_processrepo__t which creates git objects.

Test Plan: $ ./precommit.sh
WIP: conduitmock
WIP: abdt_git
fixup! WIP: abdt_git
Arcyd testbed: reduce delay in run_arcyd_multi.sh

Reduced delay from 5 secs to 2 secs

Test Plan: testbed/arcyd/ $ ./run_arcyd_multi.sh
fixup! WIP: abdt_git
fixup! WIP: abdt_git
fixup! WIP: abdt_git
fixup! WIP: abdt_git
fixup! WIP: abdt_git