[CDH4] Disable admission control to work around HUE-994

On CDH4, Hue does not close queries (HUE-994), so queries
submitted through Hue will never be released in the admission controller
and eventually all queries will be rejected. This disables admission
control on CDH4 to work around this problem.

Change-Id: I1bb1707b1d2c4f8c041b6521e715aa9f7fabc182
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2399
Tested-by: jenkins
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: Matthew Jacobs <mj@cloudera.com>