Common standard for assertEqual usage in neutron unit testing

This BP comes to define a standard usage of assertEqual() function in Neutron unit testing code.

Neutron Unit Testing code uses assertEqual() function in all it's unit testing modules and classes.
The signature of this function is assertEqual(self, expected, observed, message='')
Values for comparison should be in order of expected value comes first, actual value comes after.

There is no standard of using this function in Neutron unit testing.
Function is called in both ways, assertEqual(expected, observed) and assertEqual(observed, expected)
while the second case seems to be preferable.

Neutron unit testing code should have standard usage of assertEqual() function
that fits its assertEqual(expected, observed) signature