vml_set_mode/vml_get_mode should round-trip

[oleksandr-pavlyk]

Currently:

In [1]: import mkl

In [2]: mkl.vml_get_mode()
Out[2]: ('ha', 'default', 'default')

In [3]: mkl.vml_set_mode(*mkl.vml_get_mode())
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
ValueError: Variable: <default> not in {'on': 2621440, 'off': 1310720}
Exception ignored in: 'mkl._py_mkl_service.__mkl_str_to_int'
ValueError: Variable: <default> not in {'on': 2621440, 'off': 1310720}
Out[3]: ('ha', 'default', 'default')