Switch from x/net/context to context made "go vet" see the previously
unseen errors:
> cli/command/container/start.go:57::error: the cancelFun function is
> not used on all paths (possible context leak) (vet)
> cli/command/container/start.go:63::error: this return statement may be
> reached without using the cancelFun var defined on line 57 (vet)
> cli/command/container/run.go:159::error: the cancelFun function is not
> used on all paths (possible context leak) (vet)
> cli/command/container/run.go:164::error: this return statement may be
> reached without using the cancelFun var defined on line 159 (vet)
Do call the cancel function.
Note we might end up calling it twice which is fine as long as I can see
from the Go 1.10 source code.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>