python pmapi: add __str__ handler for class pmLabelSet
python pmapi: add __str__ handler for class pmLabelSet

This makes class pmLabelSet more pythonic by adding a __str__
handler - so you can walk the list of pmLabelSets returned by
pmLookupLabels and friends, and just print each list member as
a JSON string. See example in man page for pmlookuplabels(3)
under the new "PYTHON EXAMPLE" section.

Future: a dict converter might be handy too.

modified:   src/python/pcp/pmapi.py

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