Missing rados API components: function rados_read_op_exec_user_buf

[phlogistonjohn]

The rados API implements function(s) below but go-ceph does not:

• rados_read_op_exec_user_buf

This issue has been filed to track implementing this missing
functionality in the appropriate package within go-ceph.
Please refer to the Ceph C API for details about the function(s)
in question.

NOTE: This issue was generated by a script.
If the content is innacurate or wording seems a bit odd
please excuse the script and blame the creator @phlogistonjohn