erasure-code: refactor jerasure Liberation parameters checks

erasure-code: refactor jerasure Liberation parameters checks

Create a virtual function to check for each parameter for Liberation
and its derivations Liber8tion and BlaumRoth. The code is moved around
but is unmodified.

A function reseting the parameters to sane defaults when an error
occurs is introduced. It is slightly different from the code that was
duplicated in Liberation and BlaumRoth. In both cases it now resets w.
It is a noop for Liber8tion because the user cannot modify this
parameter which is always set to the default.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>