Test case for OLT disable / delete

An issue with OLT disable / delete (VOL-2347) is preventing per-patchset sanity tests from passing consistently.  Until that issue is resolved, we are turning off OLT delete as part of that sanity test.  However, once the issue is fixed, we want to re-enable OLT device delete to run during the per-patch sanity test.  It should run in its own distinct test case rather than be embedded in the test cleanup stage to make failures easier to see.

It is also the case that other tests may want to disable / delete the OLT as part of their setup (e.g., if the test wants to start with a clean system).  Take this into account when refactoring the tests.