Add RHEV to vm_info map. (LP: #1884116)

[simpoir]

Testing instructions:

The easy way to verify this is to run the unit tests.
The proper way to verify this is to spawn a kvm and virsh edit

and add a <smbios mode="sysinfo"/> under <os>, and a sysinfo block after </os>:

<sysinfo type='smbios'>
  <bios>
    <entry name='vendor'>LENOVO</entry>
  </bios>
  <system>
    <entry name='manufacturer'>Red Hat</entry>
    <entry name='product'>RHEV Hypervisor</entry>
    <entry name='version'>7.8-2.el7ev</entry>
  </system>
  <chassis>
    <entry name='manufacturer'>Red Hat</entry>
  </chassis>
</sysinfo>

The other way is to have an RHEV install.

[maxiberta]

LGTM