Bug 1464461

Description of problem:
The "hosted-engine --upgrade-appliance" report unsupportred path when upgrading from RHEV 3.6 to RHV 4.0

Version-Release number of selected component (if applicable):
ovirt-hosted-engine-setup-2.1.0.6-1.el7ev.noarch

How reproducible:
100%

Steps to Reproduce:
1.Upgrade from latest RHEL host nad latest RHEV-M 3.6 to 40

Actual results:
hosted-engine --upgrade-appliance
[ INFO  ] Stage: Initializing
[ INFO  ] Stage: Environment setup
          During customization use CTRL-D to abort.
         
          ==================================================================================
          Welcome to the oVirt Self Hosted Engine setup/Upgrade tool.
         
          Please refer to the oVirt install guide:
          https://www.ovirt.org/documentation/how-to/hosted-engine/#fresh-install
          Please refer to the oVirt upgrade guide:
          https://www.ovirt.org/documentation/how-to/hosted-engine/#upgrade-hosted-engine
          ==================================================================================
          Continuing will upgrade the engine VM running on this hosts deploying and configuring a new appliance.
          If your engine VM is already based on el7 you can also simply upgrade the engine there.
          This procedure will create a new disk on the hosted-engine storage domain and it will backup there the content of your current engine VM disk.
          The new el7 based appliance will be deployed over the existing disk destroying its content; at any time you will be able to rollback using the content of the backup disk.
          You will be asked to take a backup of the running engine and copy it to this host.
          The engine backup will be automatically injected and recovered on the new appliance.
          Are you sure you want to continue? (Yes, No)[Yes]: 
          Configuration files: []
          Log file: /var/log/ovirt-hosted-engine-setup/ovirt-hosted-engine-setup-20170623152821-ikhe8k.log
          Version: otopi-1.6.2 (otopi-1.6.2-1.el7ev)
[ INFO  ] Detecting available oVirt engine appliances
[ INFO  ] Stage: Environment packages setup
[ INFO  ] Stage: Programs detection
[ INFO  ] Stage: Environment setup
[ INFO  ] Checking maintenance mode
[ INFO  ] The engine VM is running on this host
[ INFO  ] Stage: Environment customization
[ INFO  ] Answer file successfully loaded
          Enter engine admin password: 
          Confirm engine admin password: 
[ INFO  ] Acquiring internal CA cert from the engine
[ INFO  ] The following CA certificate is going to be used, please immediately interrupt if not correct:
[ INFO  ] Issuer: C=US, O=sbr-virt.gsslab.brq.redhat.com, CN=rhodain-rhel7-36-m-upgrade.sbr-virt.gsslab.brq.redhat.c.82144, Subject: C=US, O=sbr-virt.gsslab.brq.redhat.com, CN=rhodain-rhel7-36-m-upgrade.sbr-virt.gsslab.brq.redhat.c.82144, Fingerprint (SHA-1): A0D381ACB005FD2F34C2FADF6E6339CEC31144E
[ INFO  ] Bridge ovirtmgmt already created
[WARNING] Unable to uniquely detect the interface where Bridge ovirtmgmt has been created on, [u'eth0', u'vnet0'] appear to be valid alternatives
[ INFO  ] Checking SPM status on this host
[ INFO  ] Connecting to the Engine
[ INFO  ] This upgrade tool is running on the SPM host
          The following appliance have been found on your system:
          	[1] - The RHEV-M Appliance image (OVA) - 4.0.20170307.0-1.el7ev
          	[2] - Directly select an OVA file
          Please select an appliance (1, 2) [1]: 
[ INFO  ] Verifying its sha1sum
[ INFO  ] Checking OVF archive content (could take a few minutes depending on archive size)
[ INFO  ] Checking OVF XML content (could take a few minutes depending on archive size)
          Please specify the size of the VM disk in GB: [50]: 
[ INFO  ] Connecting to the Engine
[ INFO  ] The hosted-engine storage domain has enough free space to contain a new backup disk.
[WARNING] On the hosted-engine disk there is not enough available space to fit the new appliance disk: required 50GiB - available 20GiB. 
          This upgrade tool can resize the hosted-engine VM disk; before resizing a backup will be created.
           Are you sure you want to continue? (Yes, No)[Yes]: 
[ INFO  ] Checking version requirements
[ INFO  ] Hosted-engine configuration is at a compatible level
[ INFO  ] Connecting to the Engine
[ INFO  ] All the datacenters and clusters are at a compatible level
[WARNING] Unsupported upgrade path
          This procedure has been designed and tested only for upgrading the engine VM from ['3.6'] to ['4.0'].
          Any other usage is highly experimental and potentially dangerous:
            Current engine: 3.6
            Selected appliance: 4.0.20170307.0-1.el7ev
          Do you want to abort the upgrade process? (Yes, No) [Yes]: 


Expected results:
"[WARNING] Unsupported upgrade path" is not reported