examples/nodestat: Fix None comparison
examples/nodestat: Fix None comparison

"is" compares for "points to the same object", which for strings is the
same as comparing the byte sequence itself as Python hashes each strings
to only stores a unique copy of each string.

> examples/nodestats.py:86:43: F632 use ==/!= to compare constant literals (str, bytes, int, float, tuple)
> examples/nodestats.py:91:12: F632 use ==/!= to compare constant literals (str, bytes, int, float, tuple)
> examples/nodestats.py:94:40: F632 use ==/!= to compare constant literals (str, bytes, int, float, tuple)

Use "==" and "!=" for string comparsion.

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

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