webadmin: deny resizing hook content textarea

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

Change-Id: I70be9768c5e5a250e16dc57c2a125b9978a86d1d
Bug-Url: https://bugzilla.redhat.com/975805
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>