pmda.py: add support for logfile and helptext file in PMDA __init__
pmda.py: add support for logfile and helptext file in PMDA __init__

Adds support for optional log and helptext file names in the PMDA class,
i.e. __init__(self, name, domain, logfile=None, helpfile=None)
If not specified, both logfile and helpfile fall back to their original
defaults (name + ".log" and $PCP_PMDAS_DIR/name/"help", respectfully).

Existing python PMDAs that do not specify logfile or helpfile continue
to use the defaults, no change.

modified:   src/python/pcp/pmda.py

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