Updated test to handle new format of cpumask

The file /sys/bus/workqueue/devices/writeback/cpumask may contain
a comma separated list of hex numbers (00000000,00000fff). Now
test_partition.py can handle this.

Also removed some code that was not used.

Signed-off-by: Andreas Sundström <andreas.sundstrom@enea.com>
Removed whitelists from test_partition.py

The test case where dependent of having whitelists defined for targets
to run on. This patch removes these whitelists, making it possible to run
on more targets. The test becomes a bit less strict but gets easier to
maintain.

Signed-off-by: Andreas Sundström <andreas.sundstrom@enea.com>