[autotest] Check for the proper variable in a provision control file.

Ah, artifacts of old refactoring.  We don't pass down the provisioning
labels anymore, just the value, and thus the variable names changed, but
the string never did...

This worked because the provisioning control segment also sets
provision_labels, so if provision_labels is set it means value will end
up getting set also, but we should be testing for the actual variable
that we're going to use.

Also making TestError actually exist.

BUG=chromium:267139
TEST=Reran provision test with/without value

Change-Id: I02cf4506a8c38a23cd00c6650a6bbaf6f3d1856b
Reviewed-on: https://gerrit.chromium.org/gerrit/64269
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
1 file changed