virStream.sendAll() fix raising an undeclared var

The exception is raised from the variable 'e', which was undeclared in
this context. Used code that is compatible with old and new Python
versions.

libvirt-override-virStream.py

@@ -76,6 +76,7 @@
             try:
                 got = handler(self, 1024*64, opaque)
             except:
+                e = sys.exc_info()[1]
                 try:
                     self.abort()
                 except: