Synchronise the KVs list for scanner results
Synchronise the KVs list for scanner results

Synchronises the list that holds the KeyValues that have been produced
by the scanner callbacks. The list is accessed from multiple threads at
a time and wasn't thread-safe, causing inconsistent results and partial
loss of data in the response.

Relates to: #1753
Resolves: #1760

MadDogTechnology/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,OpenTSDB/opentsdb,OpenTSDB/opentsdb