webadmin: prestarted VM and increase num of VMs restyled

Edit pool dialog, prestarted VMs and increase num of VMs incorreclty styled.
The sizes where hard coded. The problem become visible after the dialog has
been shrinked. After unfolding the "Advanced Parameters", the scroll bar
appeared effectivly shrinking the width of the dialog. The hard-coded widths
where not able to respond to this.

Change-Id: Iaa4130b1076162a09a3189f569b0a6a3da434d39
Bug-Url: https://bugzilla.redhat.com/879334
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>