Sorted the operations in TimeStats display.
Sorted the operations in TimeStats display.

Details:
- CHanged __str__() to sort the operations by decreasing average time.
- Made the example output consistent with that and more realistic.
- Rearranged some code using .format() to be recognized by coverage tool.

Signed-off-by: Andreas Maier <38dbb04957d222ea6ce72de72413b1e55e665472@de.ibm.com>

zhmcclient/python-zhmcclient,zhmcclient/python-zhmcclient