Fix test case skipping logic: if < py2.7 then no OrderedDict, so skip.

For ordered execution, PyDSL requires py2.7 or above. Although, it's
possible to make it work with a third-party OrderedDict implementation
like the yaml renderer does..., this is not bothered here.
Merge pull request #3426 from kjkuan/pydsl-test-case-fix2

Fix test case skipping logic: if < py2.7 then no OrderedDict, so skip.