fixes #4123 - libvirt imaging support using backing volumes

fixes #3697, #3701 - more comprehensive field validations

Fixes #3481 - Don't have to set a hostname for each interface, but it must be unique if it is set.

fixes #2741 - rails 3 syntax

fixes #2411 - move STI models in /models and /lib/foreman/models to sub-folders

fixes #2713 - do not update nics table on every host update as a workaround to bug #2489

fixes #2489 - fixes BMC password caused by rails bug accepts_nested_attributes_for and serialized child field

fixes #2325 No A record created in domain when provisioning image based vm

fixes #426 expose BMC information in foreman UI

Signed-off-by: Ohad Levy <ohadlevy@gmail.com>

This patch also adds an abstracted power management class for both VM
and BM

Feature #2368 - use N_ for model validators

As per https://github.com/grosser/fast_gettext/wiki/activerecord