tests: convert tests to nose

Signed-off-by: Michael Walle <michael.walle@kontron.com>
convert some functions to properties

Instead of providing setters and getters use the python property
annotation.

Signed-off-by: Michael Walle <michael.walle@kontron.com>
minor syntactical changes

Don't convert to list before passing the iterable to join().

Signed-off-by: Michael Walle <michael.walle@kontron.com>
cli_tool: fix spi command

Signed-off-by: Michael Walle <michael.walle@kontron.com>
better python 3 compatibility

Signed-off-by: Michael Walle <michael.walle@kontron.com>