CA-184525: Change set of datasources exported by xcp-rrdd-iostat
CA-184525: Change set of datasources exported by xcp-rrdd-iostat

Remove `io_throughput_read`, `io_throughput_write` and
`io_throughput_total`  and add `read`, `write`, `read_latency` and
`write_latency`. The new datasources correspond to the datasources
which used to be exported by xcp-rrdd, and which are understood by
XenCenter.

Signed-off-by: John Else <37b74501daa612e48fea94f9846ed4ddeb6a8f07@citrix.com>

johnelse/rrdd-plugins,johnelse/rrdd-plugins