#4069 [HHQ-56] Add I/O Device service

[Hyperic Team]

http://jira.hyperic.com/browse/HHQ-56
2.7.0 includes pdk/plugins/examples/io-device-plugin.xml, using pdk/scripts/device_iostat.pl wrapper to get metrics from iostat -x

This only works on Linux with 2.6+ kernels and iostat installed, but this could be auto-discovered to avoid creating the services by hand.

Should also explore support for other platforms.