Add instructions support to PublicError
When long additional text should follow the error message, one can
supply instructions parameter to a class derived from PublicError.
This will cause following text added to the error message:
Additional instructions:
<additional text>
`instructions' optional parameter could be a list or anything that coerces
into unicode(). List entries will be joined with '\n'.
https://fedorahosted.org/freeipa/ticket/3167