thread: print error for io_devices at lib fini

All io_devices should be unregistered before the
application exits.  If not, print an error message
for each io_device that still exists.

Eventually we may want to assert() if any io_devices
are found, but for now we'll just stick with the
error message.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: If017edf40fc2904ed772bc1c6124f06fc9b49bcd

Reviewed-on: https://review.gerrithub.io/433202


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>