Lock updating to the push branch for only when we force an update.
Lock updating to the push branch for only when we force an update.

This addresses the issue where a gerrit remote doesn't yet exist,
thus the repo is pointlessly wiped.

Fallout from chumped chumped fix: Icf6a88cc201f2e6.

BUg=None
TEST=None

Change-Id: I07c9ee695d61fd2787c3b0d3e6240e5623b04065
Reviewed-on: https://gerrit.chromium.org/gerrit/23993
Reviewed-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>

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