Check for errors when trying to create the auth token file (#447)
Check for errors when trying to create the auth token file (#447)

* Check for errors when trying to create the auth token file
* Close the file right away, instead of closing with `defer`

The file is not being used after it's created/opened, so there's no
reason to defer the closing.

danielfm/kube-aws,c-knowles/kube-aws,iflix-letsplay/kube-aws,mumoshu/kube-aws,camilb/kube-aws,iflix-letsplay/kube-aws,HotelsDotCom/kube-aws,camilb/kube-aws,c-knowles/kube-aws,kubernetes-incubator/kube-aws,HotelsDotCom/kube-aws,mumoshu/kube-aws,everpeace/kube-aws,everpeace/kube-aws,kubernetes-incubator/kube-aws,danielfm/kube-aws