Tee: immediately exit on completion.
Tee: immediately exit on completion.

We don't care about Process's teardown behaviour (not applicable
to us), nor do we particularly wish to show a KeyboardInterupt tb
from w/in the Tee process itself.

We just want Tee to die.  Thus make it die w/ post haste.

BUG=None
TEST=ctrl+c a cbuildbot instance.

Change-Id: I98bca675bfca25179d76e84c22cfd89361eadd34
Reviewed-on: https://gerrit.chromium.org/gerrit/20048
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Commit-Ready: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>

chadversary/chromiumos.chromite,zhang0137/chromite,zhang0137/chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,coreos/chromite,bpsinc-native/src_third_party_chromite