erp5_core: Only search for ERP5 Login

   The implementation only works with ERP5 Login, since it is the only portal type that
   holds password in ERP5. Other implementations are password-less: Certificate Login,
   Google Login and Facebook Login, so they cannot have their password reset anyway.

   It is overkill split the login on multiple categorization, to use some portal group (ie:
   getPortalLoginPortalTypeThatCanResetPassord...) until we have a a clear usecase.