webadmin: disable resizing hook content textarea

Disabling the resize property of the textarea which
will show the hook content.

Change-Id: I6f8d4ee4c3cb06dc5929efd94c300316b13071e3
Bug-Url: https://bugzilla.redhat.com/975805
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>