The probePodIPs sometimes (depending on configuration) will return a
true for noop when in fact there are changes.  This is due to changes to
the healthy endpoints being possible outside of probing.

- Change the unchanged value to just compare the existing healthy set
  with the new one.
- Add tests to cover most of the different cases of behavior for the
  probePodIPs function.

NOTE: There is one test case `no changes without probes` that now shows
different behavior than prior code.  Prior code would return a false for
noop.  After reviewing the calling code this did not seem to make sense
for a non-probing non-updating call to update the endpoints (given the
other non-probe changes are now accounted for).  So this was left as it
is now with the simple unchanged value logic.

- Rename one test case
- Move both rw and fakeRT inside test function