Description of problem:
When using either the 'rbd export' or 'rbd export-diff' commands with the '--rbd-concurrent-management-ops' flag no impact on performance is observed.

Sample output from current attempt:

# snapshot created for initial export
$ rbd snap ls rbd/nas7-rds-stg1
SNAPID NAME             SIZE 
  1106 161224-0935 102400 GB

$ rbd info rbd/foobar@161224-0935
rbd image 'foobar':
        size 102400 GB in 26214400 objects
        order 22 (4096 kB objects)
        block_name_prefix: rbd_data.5f059d238e1f29
        format: 2
        features: layering
        flags: 
        protected: False

$ rbd export-diff --rbd-concurrent-management-ops 50 rbd/foobar@161224-0935 - | pv | rbd import-diff --rbd-concurrent-management-ops 50 - expandtest/foobar
Importing image diff: 1% complete...    1TiB 7:39:35 [37.2MiB/s]
Importing image diff: 2% complete...   2TiB 19:53:12 [36.7MiB/s]
Importing image diff: 3% complete...   3TiB 27:30:54 [43.2MiB/s]
Importing image diff: 4% complete...   4TiB 34:33:08 [7.97MiB/s]
Importing image diff: 5% complete...   5TiB 41:44:14 [42.4MiB/s]

Version-Release number of selected component (if applicable):
0.94.x (will request specific ceph -v) 

How reproducible:
Always 

Steps to Reproduce:
1. Create snapshot from an rbd 
2. Export/import and specify the '--rbd-concurrent-management-ops' flag, for example:

rbd export-diff --rbd-concurrent-management-ops 50 rbd/foobar@161224-0935 - | pv | rbd import-diff --rbd-concurrent-management-ops 50 - expandtest/foobar

Actual results:
Slow performance when performing an rbd export/export-diff

Expected results:
Performance should be higher when '--rbd-concurrent-management-ops' is set to a high value.  A ceph cluster should have a ton of parallelism available to it.

Additional info:
* Providing fio profile and job output which exhibits the concurrency expected in the cluster vs the image diff import above.
* Debug data is en route
* It's also worth noting that if 'export-diff' truly does not support 'rbd-concurrent-management-ops' even though it appears to be present in the code: 

ceph/src/tools/rbd/action/ExportDiff.cc:
168   ExportDiffContext edc(&image, fd, info.size,
169                         g_conf->rbd_concurrent_management_ops, no_progress);
170   r = image.diff_iterate2(fromsnapname, 0, info.size, true, whole_object,
171                           &C_ExportDiff::export_diff_cb, (void *)&edc);

The customer has also seen the same behavior on just 'export'.