CSV Format

[rlankfo]

According to the documentation, we should be able to get QueryPerf responses back in CSV format. This would be preferred to the default XML format.

When attempting this against a live environment, I'm seeing the following panic from govmomi:

panic: expected type *types.PerfEntityMetric, got: *types.PerfEntityMetricCSV

goroutine 52 [running]:
github.com/vmware/govmomi/performance.(*Manager).ToMetricSeries(0xc000345180, 0x11c66c0, 0xc000036088, 0xc000525a40, 0x2, 0x2, 0xc, 0xc000524420, 0xc000524400, 0x1, ...)
        /home/rlankfo/go/pkg/mod/github.com/vmware/govmomi@v0.27.2/performance/manager.go:453 +0x745
github.com/grafana/vmware_exporter/vsphere.(*vsphereCollector).collect(0xc0002c5ca0, 0x11c66c0, 0xc000036088, 0xc0003b1e40, 0x0, 0x0, 0x0, 0x0, 0xc000524420, 0xc000524400, ...)
        /home/rlankfo/vmware_exporter/vsphere/collector.go:168 +0x490
github.com/grafana/vmware_exporter/vsphere.(*vsphereCollector).collectChunk(0xc0002c5ca0, 0x11c66c0, 0xc000036088, 0xc000033b00, 0xc0003b1e40, 0x0, 0x0, 0x0, 0x0, 0xc000524420, ...)
        /home/rlankfo/vmware_exporter/vsphere/collector.go:141 +0x328
github.com/grafana/vmware_exporter/vsphere.(*vsphereCollector).collectResource.func1(0xc0004752d0, 0xc0003e2a40, 0xc0002c5ca0, 0x11c66c0, 0xc000036088, 0xc000033b00, 0xc0003b1e40, 0x0, 0x0, 0x0, ...)
        /home/rlankfo/vmware_exporter/vsphere/collector.go:111 +0x13a
created by github.com/grafana/vmware_exporter/vsphere.(*vsphereCollector).collectResource
        /home/rlankfo/vmware_exporter/vsphere/collector.go:108 +0x7fa

Here's a link to a Java example in the docs that uses CSV format: https://developer.vmware.com/docs/1132/vsphere-web-services-sdk-programming-guide/doc/PG_Performance.18.4.html

The document also talks about casting PerfEntityMetricBase objects to use the CSV format:

When you specify “csv” format, you must cast the returned PerfEntityMetricBase objects into PerfEntityMetricCSV
objects. Both the sampling information and the collected data are encoded as comma-separated values suitable for
display in tabular format.

I thought govmomi would probably handle the type conversions / casting but doesn't seem to be the case. Need to investigate this further.