interop: interop functions should not call context.Background() for RPCs

[dfawley]

E.g.

grpc-go/interop/test_utils.go

Lines 82 to 83 in 70f1a40

	func DoEmptyUnaryCall(tc testgrpc.TestServiceClient, args ...grpc.CallOption) {
	reply, err := tc.EmptyCall(context.Background(), &testpb.Empty{}, args...)

This function and all others in this file should accept a context, which would allow passing RPC timeouts, metadata, etc. context.Background is really only supposed to be called by main/TestXyz functions wherever possible.

[Aditya-Sood]

hi @dfawley, can I pick this up?

[dfawley]

@Aditya-Sood Yes, that would be great! But note that we are going to be moving stress/* to interop/stress/*, so you might want to wait until that's done, first.

[Aditya-Sood]

I think that's done with the merge of #6769 now?

[arvindbr8]

@Aditya-Sood -- Yes that's right!