Fix order of arguments in assertEqual

Some tests used incorrect order assertEqual(observed, expected).

The correct order expected by testtools is...

    def assertEqual(self, expected, observed, message=''):
        """Assert that 'expected' is equal to 'observed'.

        :param expected: The expected value.
        :param observed: The observed value.
        :param message: An optional message to include in the error.
        """

The string length of the sum of the results of repr(expected) and
repr(observed) is greater than 70, then, MismatchError message is
changed, as below.

  Ex.:
        raise mismatch_error
    MismatchError: !=:
    reference = '_123456789_123456789_bar'
    actual    = '_123456789_123456789_123456789_123456789_123456789'

Change-Id: Id02ddfb2ca03df7f432cff67a7bed182cccc4924
Closes-Bug: #1259292
Merge "Fix order of arguments in assertEqual"