(#136) - skip "Testing conflicts" in _changes

Cloudant doesn't currently support conflicts=true on the _changes feed.
Skipping this test for now until I find out more about why/whether it
will be supported.
(#136) - Cloudant fixes for attachment tests

We cannot rely on an ordered update sequence in Cloudant.
Instead, request the _changes feed following the initial docment update
using the "since" parameter. There is still potential for this to fail
because _changes may return entries before that specified by "since" -
the guarantee is that all entries following "since" will be returned.

Possibly one to review if we find that the test fails occasionally
(for me it is stable).