Fix faulty error checking.
Fix faulty error checking.

Specifically, ignore the exit code from trying to wipe pushurl; the
setting may not exist.

BUG=None
TEST=None

Change-Id: If419a0dbe73a54aff3ce46e753206353ffd7f1a4
Reviewed-on: https://gerrit.chromium.org/gerrit/19320
Commit-Ready: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Reviewed-by: Chris Sosa <959d3d631fb6f17f1b07f751372041a1edb210d1@chromium.org>

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