python: return dictionary without value in case of no blockjob
python: return dictionary without value in case of no blockjob

Currently, when there is no blockjob, dom.blockJobInfo('vda')
still reports error because it doesn't distinguish return value 0 from -1.
libvirt.libvirtError: virDomainGetBlockJobInfo() failed

virDomainGetBlockJobInfo() API return value:
 -1 in case of failure, 0 when nothing found, 1 found.

And use PyDict_SetItemString instead of PyDict_SetItem when key is
of string type. PyDict_SetItemString increments key/value reference
count, so call Py_DECREF() for value. For key, we don't need to
do this, because PyDict_SetItemString will handle it internally.

fabianfreyer/libvirt,zippy2/libvirt,eskultety/libvirt,zippy2/libvirt,eskultety/libvirt,olafhering/libvirt,crobinso/libvirt,rlaager/libvirt,libvirt/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,cbosdo/libvirt,datto/libvirt,VenkatDatta/libvirt,elmarco/libvirt,andreabolognani/libvirt,agx/libvirt,zippy2/libvirt,taget/libvirt,agx/libvirt,eskultety/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,taget/libvirt,libvirt/libvirt,nertpinx/libvirt,datto/libvirt,shugaoye/libvirt,taget/libvirt,rlaager/libvirt,elmarco/libvirt,jfehlig/libvirt,agx/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,shugaoye/libvirt,cbosdo/libvirt,agx/libvirt,crobinso/libvirt,agx/libvirt,VenkatDatta/libvirt,elmarco/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,nertpinx/libvirt,cbosdo/libvirt,olafhering/libvirt,nertpinx/libvirt,jardasgit/libvirt,eskultety/libvirt,elmarco/libvirt,jfehlig/libvirt,jardasgit/libvirt,rlaager/libvirt,eskultety/libvirt,rlaager/libvirt,libvirt/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,libvirt/libvirt,shugaoye/libvirt,shugaoye/libvirt,elmarco/libvirt,datto/libvirt,jardasgit/libvirt,zhlcindy/libvirt-1.1.4-maintain,rlaager/libvirt,zhlcindy/libvirt-1.1.4-maintain,olafhering/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,datto/libvirt,andreabolognani/libvirt,taget/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,crobinso/libvirt,crobinso/libvirt,cbosdo/libvirt,zhlcindy/libvirt-1.1.4-maintain,olafhering/libvirt,zhlcindy/libvirt-1.1.4-maintain,datto/libvirt,andreabolognani/libvirt,taget/libvirt,cbosdo/libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain