libminijail_unittest: fix unittests for consumestr
libminijail_unittest: fix unittests for consumestr

consumestr changed the behavior of unmarshal and the unittest
needed to be updated to reflect it.

TEST=FEATURES=test emerge-x86-alex chromeos-minijail (with pending cl to add test support)
BUG=none

Change-Id: I29af4b2103b081c749efbb9b2c6a08e6ca3f0b03
Reviewed-on: https://gerrit.chromium.org/gerrit/10534
Commit-Ready: Will Drewry <72416dde44ea762d19e3a7a555e3b59ce98f8eea@chromium.org>
Reviewed-by: Will Drewry <72416dde44ea762d19e3a7a555e3b59ce98f8eea@chromium.org>
Tested-by: Will Drewry <72416dde44ea762d19e3a7a555e3b59ce98f8eea@chromium.org>

omegaup/minijail,omegaup/minijail,omegaup/minijail,omegaup/minijail