Move 'value sources' to the short description field

[BurtBiel]

they are currently in the long description field, which doesn't look good by itself.

[tjprescott]

Burt Bielicki (@BurtBiel) can you post an example of the problem?

[BurtBiel]

Today value sources is only used by vm/vmss create:

--image                       : OS image (URN alias, URN or URI).  Default: Win2012R2Datacenter.
        URN aliases: CentOS, CoreOS, Debian, openSUSE, RHEL, SLES, UbuntuLTS, Win2008SP1,
        Win2012Datacenter, Win2012R2Datacenter.
        Example URN: MicrosoftWindowsServer:WindowsServer:2012-R2-Datacenter:latest.
        Example URI: http://<storageAccount>.blob.core.windows.net/vhds/osdiskimage.vhd.
        Values from: az vm image list, az vm image show.

If there was no long description is would look like this:

--image                       : OS image (URN alias, URN or URI).  Default: Win2012R2Datacenter.
        Values from: az vm image list, az vm image show.

In this case, value sources shouldn't appear in the long description field. They should be in the short description field so we don't unnecessarily break the help flow

The desired output look like:

--image                       : OS image (URN alias, URN or URI).  Default: Win2012R2Datacenter.  Values                
                                      from: az vm image list, az vm image show.