OpenTSDBWriter: add mergeTypeNamesTags setting to enable multiple tags, when false, while keeping the default, single, concatenated tag.
Added tests for new mergeTypeNamesTags setting, and increase overall coverage.
Merge pull request #124 from artnaseef/addMergeTypeNamesTags

Add mergeTypeNamesTags setting to OpenTSDBWriter to support merged (default) or split tags based on type names