[improvement] better logging

[EgorBu]

Hi,
It would be nice to improve the logging message so it's easy to understand what was the reason of failure.
Example:

[2018-11-28T12:41:12.035318241+01:00]  INFO streaming client call finished app=lookout-sdk duration=30m0.000160806s error=rpc error: code = DeadlineExceeded desc = Deadline Exceeded grpc.code=DeadlineExceeded grpc.method=NotifyPushEvent grpc.service=pb.Analyzer grpc.start_time=2018-11-28T12:11:12+01:00 source=grpchelper/logger.go:19 span.kind=client system=grpc
[2018-11-28T12:41:12.035542004+01:00] ERROR analysis failed analyzer=test-analyzes app=lookout-sdk error=rpc error: code = DeadlineExceeded desc = Deadline Exceeded provider= source=server/server.go:275

it appeared during push event but it's hard to guess that analyzer_push should be modified in configuration until you read https://github.com/src-d/lookout/blob/master/docs/configuration.md#advanced-fine-tuning

[EgorBu]

and one more thing will be super useful

[2018-12-02T14:16:19.772976312Z]  INFO streaming client call finished app=lookout-sdk duration=5m42.173435491s error=rpc error: code = Internal desc = <class 'ValueError'>: b'  <Menu.Item icon="edit" secondaryText="\xe2\x8c' has type str, but isn't valid UTF-8 encoding. Non-UTF-8 strings must be converted to unicode objects before being added. grpc.code=Internal grpc.method=NotifyPushEvent grpc.service=pb.Analyzer grpc.start_time=2018-12-02T14:10:37Z source=grpchelper/logger.go:19 span.kind=client system=grpc
[2018-12-02T14:16:19.773178201Z] ERROR analysis failed analyzer=test-analyzes app=lookout-sdk error=rpc error: code = Internal desc = <class 'ValueError'>: b'  <Menu.Item icon="edit" secondaryText="\xe2\x8c' has type str, but isn't valid UTF-8 encoding. Non-UTF-8 strings must be converted to unicode objects before being added. provider= source=server/server.go:275

report information about the file caused the error.

[smacker]

@EgorBu we don't know which file caused the error. Consider pseudo analyzer:

def review_request(r):
  contents = []
  for change in r.changes:
     contents.append(sdk.get_file_content(change))
  # no error to this point
  for content in contents:
     my_process_function(content) # raise here