library/ipadiscovery.py: New module for ipa discovery

The module is doing the same discovery that ipa-client-install is doing
internally. The results are saved into a structure named ipadiscovery for
the ansible module.

The discovery module is needed to be able to not depend on the definition
of the ipaservers group for example to get otp passwords, to be able to
join and to configure sssd and other services corretly.