fix /api/search/lookup when salting is enabled
fix /api/search/lookup when salting is enabled

When salting is enabled, the row key is expected to be "salt + tsuid",
we can construct row key and still call RowKey.metricNameAsync(), but
it's a little more efficient to directly extact metric uid from tsuid
and call TSDB.getUidName().

This fixes issue https://github.com/OpenTSDB/opentsdb/issues/568.

Signed-off-by: Chris Larsen <83037b211e1d109d6858769a113e269c3139ffd3@yahoo-inc.com>

johann8384/opentsdb,eswdd/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,johann8384/opentsdb,eswdd/opentsdb,alienth/opentsdb,alienth/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,OpenTSDB/opentsdb