Style changes for pep-8 and python-3000 compliance.
This changes the raising of exceptions from: raise Exception, value to raise Exception(value) as the first form will be removed in python-3000 and the second form is preferred now. The changes also involve a few cases of changing from raising standard exceptions and use our own ones. The new version also fixes many pylint-generated warnings, especially in ganeti-noded where I changed many methods to @staticmethod. There is no functionality changed (barring any bugs).