Revert test_rootwrap_filter to avoid python2.6 test failure

Revert test_rootwrap_filter to avoid python2.6 test failure

With oslo.rootwrap 1.3.0.0a1 which has a bug #1340792, that some filter
rules are dependent on its evaluation order, test_rootwrap_filter randomly
fail for a patch adding to etc/cinder/rootwrap.d/volume.filters with
python2.6, as evaluation order is randomly changes.

The bug in oslo.rootwrap is fixed in master branch, but is not yet
released and not available in CI. So this until new oslo.rootwrap is
released, this patch reverts the unit test to avoid to block reviews.

Change-Id: If86b6689ae36aa8810aad5b694ed43dfec1fd0c6