Suppress subsequent SIGTERMs
Suppress subsequent SIGTERMs

We do this to ensure that later SIGTERM's that land during cleanup/shutdown
code aren't unduly interupted while already shutting down.

BUG=None
TEST=kill cbuildbot twice in rapid succession.

Change-Id: I1a85d4f22b2fdd0cbfba0c54118443dea26c9300
Reviewed-on: https://gerrit.chromium.org/gerrit/19902
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Commit-Ready: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>

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