pmproxy: enclose response label name in double quotes
pmproxy: enclose response label name in double quotes

Resolves an issue psmith encountered and fixes qa/1601.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp