iostat2pcp: fix qa/975 on Fedora31 with latest iostat version
iostat2pcp: fix qa/975 on Fedora31 with latest iostat version

The iostat now in Fedora31 has additional columns for discard
metrics.  This causes the iostat2pcp tool to fail, and report
diagnostics like:  "Device: number of values? expected 6"

I've made minimal changes to make the utility work correctly
for this release (5.0.3) in this commit, but we'll want to
revisit this issue and add new disk metrics for discard into
iostat2pcp in a future release of PCP.

See https://github.com/performancecopilot/pcp/issues/855
and https://github.com/performancecopilot/pcp/issues/854

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