Move tracing to leverage opencensus

The current tracing implementation uses opentracing/Jaeger. Moving the implementation to use opencensus and still exporting to Jaeger will allow us to have flexibility to

• Support alternative backends
• Eliminate the vsock workaround using a custom exporter
• Add support for metrics using opencensus if needed
• Enable tracing even when kata-agent is running as agent/initrd.

Some early PoC code that shows how to create a custom exporter
https://github.com/mcastelino/custom_exporter

Phasing

The work will need to be done in three phases

• 1. Move from opentracing/Jaeger specific APIs to opencensus with the default Jaeger exporter
  This will still need to current vsock scaffolding but does not change any functionality. So externally nothing changes with this switch.

• 2. Switch from the default opencensus Jaeger exporter to the custom exporter
  This will remove the need for all the vsock related customizations on the VM rootfs.

• 3. Add the host side exporter service into the kata-shim (for v2). This will remove the need to run any logic on the host for tracing.