Fix perf problems and bug in 2i reformat

Add batch size parameter to control how many keys
are fixed at a time.
Add backpressure to query of bad idx entries to avoid
having the reformat process flooded with msgs.
Fixed problem with list keys and code triggering a second
scan during 2i reformat transition.
Make multi backend work with batched 2i reformats

This is WIP. Testing is not conclusive on whether it works, but it runs
to completion now.
Fix 2i reformat batch for multibackend
Make reformat-indexes print default parameters
move querying of fixed index status to seperate backend function

makes top-level fixed_indexes status on multi-backend,
which messes with stats, unncessary allowing it to be removed
Merge pull request #525 from basho/jrw-2i-reformat-status-change

move querying of fixed index status to seperate backend function
Merge pull request #523 from basho/eas-perf-fixes-to-2i-reformat

Fix perf problems and bug in 2i reformat