webadmin: display empty content for binary gluster hook

While resolving a conflicting hook, if one of the host
is having a binary hook and others are having text hook,
content from the previously selected host is shown.

This is fixed now by showing an empty content when
host with binary content is selected.

Change-Id: I6b430701474ff22c55109df3268f85fd833fe5a4
Bug-Url: https://bugzilla.redhat.com/973091
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>