If host.name value is present add it to resource labels

[kisieland]

Description:
I am proposing a change to resource translation (internal to OC).
It is motivated by the bug in stackdriverexporter, from the exporter perspective the host.name label is lost and the it is not exported by the pipeline.
I am proposing adding said label both to the node and resource labels.

Testing:
I've run unit tests for the changed library.
There seem to be so E2E failing tests, but I didn't debug them yet.

[bogdandrutu]

@kisieland why not fixing the stackdriver exporter to read the host.name from the ProcessIdentifier?

[kisieland]

I will open PR to stackdriverexporter with the proposed fix.
I restrained from it as it might introduce quite a lot of code.

[bogdandrutu]

@kisieland I can understand your point, but the translation logic does the right thing, and I would not add a hack in the core library just for one exporter bug :)

[jsuereth]

Note: Let me know if we need to tweak the specification around resources in OC => OTel. If you're using OCA protocol to ingest into OpenTelemetry collector and resources are not mapped properly to OC semantic conventions, we may want to look at that in the context of https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/compatibility/opencensus.md#resources

[kisieland]

I've opened: open-telemetry/opentelemetry-collector-contrib#2711