Description of problem: the Affinity Group created by Rest API has no labels even they are defined in the request body


Version-Release number of selected component (if applicable):
ovirt-engine-4.3.7.1-0.1.el7.noarch

How reproducible:100%


Steps to Reproduce:
1.Create Label (host or vm or both) in Compute/Clusters/Cluster/Affinity Labels tag
2.POST https://{{host}}/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8/affinitygroups
<affinity_group>
    <name>test_2</name>
    <enforcing>true</enforcing>
    <hosts_rule>
        <enabled>true</enabled>
        <enforcing>true</enforcing>
        <positive>true</positive>
    </hosts_rule>
    <positive>true</positive>
    <priority>1</priority>
    <vms_rule>
        <enabled>true</enabled>
        <enforcing>true</enforcing>
        <positive>true</positive>
    </vms_rule>
    <host_labels>
        <affinity_label id="90e8e1ee-0968-47c1-ac57-685d817179bf"/>
    </host_labels>
    <hosts/>
    <vm_labels>
        <affinity_label id="90e8e1ee-0968-47c1-ac57-685d817179bf"/>
    </vm_labels>
    <vms/>
</affinity_group>


Actual results:
The responce is 201 but the labels are missing 

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<affinity_group href="/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8/affinitygroups/724d8529-acf4-49d3-b46c-dc91478cb2ae" id="724d8529-acf4-49d3-b46c-dc91478cb2ae">
    <name>test_2</name>
    <link href="/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8/affinitygroups/724d8529-acf4-49d3-b46c-dc91478cb2ae/hostlabels" rel="hostlabels"/>
    <link href="/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8/affinitygroups/724d8529-acf4-49d3-b46c-dc91478cb2ae/vmlabels" rel="vmlabels"/>
    <link href="/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8/affinitygroups/724d8529-acf4-49d3-b46c-dc91478cb2ae/vms" rel="vms"/>
    <enforcing>true</enforcing>
    <hosts_rule>
        <enabled>true</enabled>
        <enforcing>true</enforcing>
        <positive>true</positive>
    </hosts_rule>
    <positive>true</positive>
    <priority>1</priority>
    <vms_rule>
        <enabled>true</enabled>
        <enforcing>true</enforcing>
        <positive>true</positive>
    </vms_rule>
    <cluster href="/ovirt-engine/api/clusters/9684ce59-4549-4204-bb6f-9a6f685a27c8" id="9684ce59-4549-4204-bb6f-9a6f685a27c8"/>
    <host_labels/>
    <hosts/>
    <vm_labels/>
    <vms/>
</affinity_group>


Expected results:
the group must contain labels

Additional info: