V2.1.0 hbase counters

[pinifaran]

1. added support for using hbase counters as the underlying implementation of opentsdb
2. added support for summing up detected duplicate counters (instead of discarding them)

[johann8384]

@pinifaran have you been using these changes at scale anywhere?

[pinifaran]

Yes. it already passed load tests at our lab and we're about to use it in production.

[johann8384]

@pinifaran Can you rebase this off of the NEXT branch instead of MASTER?

[johann8384]

I'm closing, because this, but I'll be looking out for a new PR based off opentsdb:next instead.

[pinifaran]

Hi, i create a new Pull Request to opentsdb:next branch:
HBase counters #758

Thanks.