Align carbon_ch with Python implementation

[github-vincent-miszczak]

carbon-relay-ng has incorrect carbon_ch implementation.

It lacks graphite-project/carbon@024f9e6#diff-1486787206e06af358b8d935577e76f5 update

It fixes #335

[Dieterbe]

for the record, the problem and fix in python are described at graphite-project/carbon#196

[robert-milan]

Thanks for your contribution! Before this can be merged unit tests need to be added to verify behavior before and after the fix, specifically focusing on the bug. Do you have time to write them?

[loitho]

Hi there,
is it possible to merge this fix ? The issue with the hashing prevents us from using the Carbonate tool which is annoying as it's very useful.

Kind regards

[robert-milan]

I don't currently have time to write the unit tests needed before merging this.

[Dieterbe]

we shouldn't break carbon-relay-ng deployments when they upgrade.
so I think we should have a config flag to control the sharding logic (by default: backwards compat with carbon-relay-ng's previous behavior, and opt-in for the new "compatible with python relay" behavior), at some point we can do the breaking change of flipping the default when we do a major release. (for extra benefit, at that point, people will have had a chance to test the new behavior)

[Dieterbe]

#477 is the reworked version of this PR.

[Dieterbe]

See #477 - thanks for the effort on this!