Delete commented codes from test_vmtasks.py

There are some commented codes in tests/benchmark/scenarios/vm/test_vmtasks.py,
and
https://github.com/stackforge/rally/blob/master/tests/benchmark/scenarios/vm/test_vmtasks.py#L85
is longer than 80. This patch removes these useless lines.

Change-Id: I7ad67742f19c2009589d8e9d7b171a3c685c53ee