webadmin: Setup Networks- unused space in unattached networks panel

Unattahced networks scrolling area should fill all available space.

Change-Id: I630c2599eceef7e4165a8728ed8e4faa52c67d22
Bug-Url: https://bugzilla.redhat.com/1068614
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>