Split logic among more hooks

This makes first wizard to remember answers from previous installation.
It detect default values for the first time.

These changes requires kafo >= 0.6.0 to work.
Update README.md
Merge pull request #5 from ares/remember_values

Remember values
Support RHEL7 as a default OS for provisioning

When staypuft host is RHEL6 then we automatically configure
RHEL7 as a default OS for provisioning.
On RHEL setup both 6 and 7