tests: split up test-rebase-obsolete.t in four pieces
The test case took 42 seconds to run the test before this patch and 12
seconds after (wall time, of course).
Differential Revision: https://phab.mercurial-scm.org/D10255
This directory is meant to cache artifacts useful for tests (such as bundle).
Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.
The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.