reset err value to SetDeadline return

As I attempt https://github.com/GoogleCloudPlatform/kubernetes/issues/1274, I notice that there could be a problem in the current code.

Regarding the fix on line 251:
If `err` is not modified between the previous `if err != nil {` and the `if err != nil {` right after the change then the if block right after the fix is dead code due to the `break` in the preceding if block. Because `err` is a local variable and it is not modified in those lines, I don't see how it could change.

Am I missing something here?

I made a PR here instead of an issue since the change is quite small.