cros_portage_upgrade: update unittest to pass again
cros_portage_upgrade: update unittest to pass again

Some git refactors in the pass broke the unittest.  Fix it.

BUG=None
TEST=`cros_portage_upgrade_unittest.py` passes

Change-Id: I233b0c583b2445a7da02512e938e6a43cee9a3b8
Reviewed-on: https://gerrit.chromium.org/gerrit/35990
Reviewed-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Commit-Ready: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

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