stream: Fix exception traceback handling
stream: Fix exception traceback handling

sys.exc_info() returns a 3-tuple (type, value, traceback). Raising just
`value` again looses the traceback information as this creates a new
exception.

Just use `raise` which re-raises the previous exception including the
original traceback.

FYI: There is a subtile difference between Python 2 and Python 3:

> try:
>     raise ValueError()
> except ValueError:
>     try:
>         raise TypeError()
>     except TypeError:
>         pass
>     raise

With Python 3 the exception environment is dropped after the exception
has been handled - as such Python 3 re-raises the outer ValueError.

With Python 2 the last (inner) exception is raised: TypeError

Signed-off-by: Philipp Hahn <8cb7a2c205789112a9f61bc3102305826b6a8db1@univention.de>

libvirt/libvirt-python,libvirt/libvirt-python,libvirt/libvirt-python