Improving API Core gRPC error reporting

[crwilcox]

While looking into googleapis/python-firestore#4 it seems gRPC reports child error details. While this is helpful, it can be a bit misleading to a user, as it will pair things like 503 (unavailable) with the text 'deadline exceeded' (error code 504) which seems strange.

I reached out to @lidizheng to discuss this and they brought up using debug_error_string: https://github.com/grpc/grpc/blob/d3e97d953b9a94d017d76a44b780bb5ca48e5840/src/python/grpcio/grpc/_channel.py#L80

We could potentially add rpc_exc.debug_error_string() to the exceptions formed at from_grpc_error:

python-api-core/google/api_core/exceptions.py

Line 484 in b4860fe

rpc_exc.code(), rpc_exc.details(), errors=(rpc_exc,), response=rpc_exc

Note: this could be verbose. An example raised:

{"created":"@1615494939.757345505","description":"xds call failed","file":"src/core/ext/xds/xds_client.cc","file_line":1260}
E0311 20:35:39.757768839  443158 xds_cluster_resolver.cc:742] [xds_cluster_resolver_lb 0x7ffb5c005550] discovery mechanism 0 xds watcher reported error: {"created":"@1615494939.757345505","description":"xds call failed","file":"src/core/ext/xds/xds_client.cc","file_line":1260}

Though in the case of the bug raised the error would look more like "receiving error from server, which is "Deadline Exceeded"."

[lidizheng]

<_InactiveRpcError of RPC that terminated with:
	status = StatusCode.UNAVAILABLE
	details = "Deadline Exceeded"
	debug_error_string = "{"created":"@1615495482.926352000","description":"Error received from peer ipv6:[::1]:50051","file":"src/core/lib/surface/call.cc","file_line":1063,"grpc_message":"Deadline Exceeded","grpc_status":14}"
>

I use the helloworld example to generate an UNAVAILABLE error with message "Deadline Exceeded", above is what the debug error string looks like. So, it doesn't use the word "server", but uses the term "peer".

[busunkim96]

This work seems like it would pair nicely with #99 (parsing error details from the trailing metadata)