Description of problem:
nbdkit tracebacks are compressed into a single line but they are just about usable if not very readable.

For example you would see an error like this:
nbdkit: python[1]: error: /var/tmp/rhvupload.Fh2Db2/rhv-upload-plugin.py: close: error: Fault reason is "Operation Failed". Fault detail is "[Cannot remove Virtual Disk. Related operation is currently in progress. Please try again later.]". HTTP response code is 409.

which can be read by manually unfolding the exception in an editor as:
nbdkit: error: ./python-exception.py: config_complete: error:
Traceback (most recent call last):
  File "./python-exception.py", line 54, in config_complete
    raise_error1()
  File "./python-exception.py", line 48, in raise_error1
    raise_error2()
  File "./python-exception.py", line 45, in raise_error2
    raise RuntimeError("this is the test string")
RuntimeError: this is the test string

Version-Release number of selected component (if applicable):
nbdkit-1.2.3-1.el7ev.x86_64