(maint) Yumrepo boolean values are case insensitive.

When handling boolean values for yum repos, a given value is downcased
before it is checked:

1. yum/config.py def parse(self, s): """Parse a string containing a boolean value. 1, yes, and true will evaluate to True; and 0, no, and false will evaluate to False. Case is ignored.
   
   :param s: the string containing the boolean value :return: the boolean value contained in *s* :raises: :class:ValueError if there is an error in parsing the boolean value """ s = s.lower() if s in ('0', 'no', 'false'): return False elif s in ('1', 'yes', 'true'): return True else: raise ValueError('invalid boolean value')

When validating these parameters we should perform a case insensitive
match to match the yum behavior.