UFAL/Shibboleth - the persistent_id is not being propagated to the backend

[milanmajchrak]

v5: netid-header = eppn,persistent-id
v7: authentication-shibboleth.netid-header = eppn

The user must be found by the persistent-id

AP:
Update the code in the ClarinShibAuthentication to process persistent-id

[milanmajchrak]

#772