webadmin: reset mouse cursor for resizable dialog

Mouse-cursor stuck on resize-image after closing
a dialog while re-sizing it.

The fix ensures that when closing the dialog the cursor
resets back to default.

Change-Id: Ib7f8168690eabf7a3c29e412978122e4e90fc6fe
Bug-Url: https://bugzilla.redhat.com/894076
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>