(#464) Facter should only be installed if necessary in os_boot.erb

This change adds the option --enablerepo=base to the yum install call
in os_boot.erb to make sure the base repo is always enabled. This is
necessary because the factor package from the puppetlabs repo depends
on other packages like virt-what for example which are only available
in the base repo.

The change should not introduce any regressions because it simply
makes sure that the base repo is enabled. If it is enabled already,
this will not make any difference.

This pull request fixes issue #464.
Merge pull request #466 from cr3/464

(#464) Facter should only be installed if necessary in os_boot.erb
(#471) Inconsistent assumption about @node_ip in models

This change fixes the broker_agent_handoff method in the models that
potentially used an empty ipaddress option when calling the agent_hand_off
method in the broker. Now, the agent_hand_off method is only called when
the @node_ip is not empty and still reports a useful error message when
it is empty.

Closes #471
Merge pull request #472 from cr3/471

(#471) Inconsistent assumption about @node_ip in models
add posibility to use 'autopart' or 'part' in redhat's kickstart
Merge pull request #474 from faja/feature/add_part_in_redhat_model

add posibility to use 'autopart' or 'part' in redhat's kickstart
Revert "add posibility to use 'autopart' or 'part' in redhat's kickstart"

This reverts commit 104b066.  Making it possible for users to customize the
partition layout is highly undesirable with the other committers, to
my surprise.

Given that, this is being reverted.  Users who want this capability are
expected to build their own model to implement it.