fix(vrtManager): a failed NVRAM copy aborts its libvirt streams

libvirt requires a stream that did not finish to be aborted before it is
freed. The NVRAM download of a shut-off move and upload_volume (NVRAM
upload, cloud-init seed) freed theirs after a failed send, receive or
finish without aborting, on the shared host connection. They abort now;
upload_volume opens its stream before it makes the volume, so the
cleanup has both.

vrtManager/instance.py

@@ -427,9 +427,14 @@ class wvmInstances(wvmConnect):
                 return None
             chunks = []
             stream = conn.wvm.newStream(0)
-            vol.download(stream, 0, 0, 0)
-            stream.recvAll(lambda _stream, data, out: out.append(data), chunks)
-            stream.finish()
+            try:
+                vol.download(stream, 0, 0, 0)
+                stream.recvAll(lambda _stream, data, out: out.append(data), chunks)
+                stream.finish()
+            except Exception:
+                with contextlib.suppress(libvirtError):
+                    stream.abort()
+                raise
             self.upload_volume(target, name, b"".join(chunks))
         return name