Sort password policy by priority
    
    'ipa pwpolicy-find' output is now sorted by priority of the policies.
    Lower position means lower priority. Global policy is then at the bottom.
    
    The changes has also affected LDAPSearch class in baseldap.py:
    LDAPSearch class sorts the search results by primary key be default
    (which is usually 'cn'). Therefor a function pointer entries_sortfn
    was added. If no sorting function exists, default sorting by primary key
    is used.
    
    Sorting function had to be introduced due to the fact that pwpolicy's
    primary key is also it's 'cn' and global policy is not allowed to have any
    priority.
    
    https://fedorahosted.org/freeipa/ticket/2045