So after banging my head a while trying to find out why this wasn't working for you, I realized that you were deploying Ubuntu 14.04.
The ability to disable_pockets was introduced in MAAS 2.1, and will only work when deploying Xenial+. This is because MAAS depends on cloud-init to do such configuration, and the cloud-init version in Trusty does not support this feature.
I'll mark this bug as low from the MAAS perspective to ensure we add a proper notification of this being the case, but I'll also add a wishlist bug for Trusty in cloud-init.
So after banging my head a while trying to find out why this wasn't working for you, I realized that you were deploying Ubuntu 14.04.
The ability to disable_pockets was introduced in MAAS 2.1, and will only work when deploying Xenial+. This is because MAAS depends on cloud-init to do such configuration, and the cloud-init version in Trusty does not support this feature.
I'll mark this bug as low from the MAAS perspective to ensure we add a proper notification of this being the case, but I'll also add a wishlist bug for Trusty in cloud-init.