pmdaprometheus: add --debug cmdline option
pmdaprometheus: add --debug cmdline option

new --debug cmdline option defaults if False. With this flag disabled,
non-error diagnostics are no longer written to the log.

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