t910*: s/repo-config/config/g; poke around possible race conditions

t910*: s/repo-config/config/g; poke around possible race conditions

Some of the repo-config => config renaming missed the git-svn
tests; so I'm just renaming them to be consisten with the
rest of the modern git.

Also, some of the newer tests didn't have 'poke' in them
to workaround race conditions on fast machines.  This adds
places where they can _possibly_ occur; but I don't have
fast enough hardware to trigger them.

Signed-off-by: Eric Wong <normalperson@yhbt.net>