Fix MIB definition
Merge pull request #22 from Metaswitch/mib-def-fixes

[No review required] Fix MIB definition
Omit OIDs if no data to return (rather than returning genError)
Code-review mark-ups
Merge pull request #23 from Metaswitch/iss59

[Reviewer: Andy] Omit OIDs if no data to return (rather than returning genError)
Change Metaswitch submodule refs to ClearwaterCore