change SHOW ENGINE ROCKSDB STATUS

[mdcallag]

For background see http://dev.mysql.com/doc/refman/5.6/en/show-engine.html

We need to change what is in SHOW ENGINE ROCKSDB STATUS. Right now it has live sst files which is a huge list with leveled compaction. For now I prefer to have it list the output from compaction stats. That probably needs to use one of:
db->GetProperty("rocksdb.stats", ...
db->GetProperty("rocksdb.cfstats", ...

---

*************************** 1. row ***************************
Type: ROCKSDB
Name: live_files
Status: cf=default name=/4908814.sst size=97853952
cf=default name=/4908812.sst size=97879865
cf=default name=/4908807.sst size=97833748
cf=default name=/4905498.sst size=1865749
cf=default name=/4905500.sst size=2670668