Description of problem:
Recent changes related to hosted-engine broke the ability to add a host to cluster with compatibility version 3.6.

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1. Define a 3.6 cluster in oVirt 4.0
2. Add a host from the webadmin
3.

Actual results:
The host cannot be added because of failed validation in the backend.

Expected results:
The host should be added.

Additional info:
There is a validation in the backend that fails addition of a host that is provided with hosted-engine deployment configuration in a cluster level below 4.0. The problem is that the webadmin always sends this deployment information.
First, the ability to provide hosted-engine deployment configuration should not be provided in the webadmin on cluster level 3.6 and should not pass any configuration to the backend.
Second, need to consider in the backend whether to consider NONE value as null in this validation.