Adds support for installing additional build host dependencies when
building IPA and overcloud host images via
'ipa_build_dib_host_packages_extra' and
'overcloud_dib_host_packages_extra'.

Support for installing additional host packages was added in
stackhpc.os-images v1.15.0 [1].

[1] https://github.com/stackhpc/ansible-role-os-images/pull/63

Change-Id: I1a05d448031cb415cec4cd601a030abdb8a5eba5