librados: Allow rados_pool_list() to get NULL buffer if len == 0

Coverity wants a NULL check for buf, but caller should be able to
pass a NULL buf and 0 len in order to get byte count of pool list.

Signed-off-by: David Zafman <david.zafman@inktank.com>
rbd: Prevent Seg fault by checking read result in snap_read_header()

Signed-off-by: David Zafman <david.zafman@inktank.com>
Improve ceph_scratchtoolpp

Minor output improvements
Disable clone_range code that was asserting

Signed-off-by: David Zafman <david.zafman@inktank.com>
librados, test: Make return values consistent across reads and writes

Fix consistency of read, write, append, write_full to return bytes read/written
Include C (rados_*) variants, C++ ctx variants
and aio get_return_value() and rados_aio_get_return_value()

Signed-off-by: David Zafman <david.zafman@inktank.com>
test: Improve testing ceph_test_rados_api_aio by checking return_values

Signed-off-by: David Zafman <david.zafman@inktank.com>
Improve aio changes
Add missed return_value checks for aio_append
Add more return_value checks (in Omap)
Testing aio as a pure EC test to see how any failures are reported