use the null buildpack instead of the java_buildpack
use the null buildpack instead of the java_buildpack

Turns out in the acceptance environment we don't get the java_buildpack
but instead java_buildpack_offline. To avoid breaking every time the
buildpack name changes and since `make_a_nora` uses the null buildpack,
i'm changing wats to use the null buildpack.

cloudfoundry/wats,cloudfoundry-incubator/wats,cloudfoundry/wats,cloudfoundry-incubator/wats,cloudfoundry/wats,cloudfoundry/wats,cloudfoundry-incubator/wats,cloudfoundry/wats,cloudfoundry-incubator/wats,cloudfoundry-incubator/wats