webadmin: Integrate VM icon into Add/Edit Network dialog

Reuse the VM icon next to the VM network checkbox, to strengthen the
visual affinity between the checkbox and its consequences in other
views.

Change-Id: I40f7c7e3088af2b1da174b6896bdfce27435b423
Bug-Url: https://bugzilla.redhat.com/1028523
Signed-off-by: Lior Vernia <lvernia@redhat.com>