OTLP gRPC exporter silently fails if scheme is not specified in endpoint

[dustyhorizon]

Issue arising from implementing #1771

Steps to reproduce
Supplying an remote collector hostname without scheme causes the OTLP exporter to silently not export spans.

opentelemetry-python/exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py

Line 210 in b3455cd

endpoint = parsed_url.netloc

parsed_url.netloc is an empty str if the scheme is not specified e.g. localhost:55680, this causes spans to not be exported to a remote collector as endpoint is empty.

What is the expected behavior?
Spans are correctly exported to remote collector via OTLP.

What is the actual behavior?
Spans are not exported to remote collector via OTLP.

Additional context
Per opentelemetry specs, it was written that the scheme must be specified in the endpoint; this library should either enforce that the scheme is supplied (fail hard if not) or assume a sane default (http?) for the purposes of using this library.

[codeboten]

Thanks for raising this issue. i did not expect url parse to set localhost in the scheme 😞

[ElementalWarrior]

For those who bump into issues with grpc exporting, you can set these environment variables for the grpc library that the exporter uses, and it will export things like the path its going to, etc.

GRPC_VERBOSITY=DEBUG
GRPC_TRACE=http