cmdrunner: remove out dir in error case too
cmdrunner: remove out dir in error case too

This is followup for
https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1802061/23/cmdrunner/command.go#315

Bug: 962804
Change-Id: Ib828c92a6e88821435fb3e863bd7383a244d71fc
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1816017
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go