Add partial 'tcbdbtune' support

This patch was taken from Incubaid/arakoon@0c548cfe971efb7 and applied
manually.

See: https://github.com/Incubaid/arakoon/commit/0c548cfe971efb78d3700e7252b09ce8d1eb7086
Merge pull request #3 from NicolasT/ARAKOON-373

Add partial 'tcbdbtune' support