Make distributable webapps depend on the clustering cache

In 4.x, in the all config the JBossWeb service itself depends on the jboss.cache:service=TomcatClusteringCache mbean. In AS 5 this is not viable, as the relevant bean is the TomcatDeployer, which can't/shouldn't depend on a deploy folder service like the cache. In any case, it's really the <distributable/> webapps that depend on the cache, not the deployer.

The TomcatDeployer should be adding a dependency on the cache to deployments where WebMetaData.getDistributable() is true (probably in superclass AbstractWarDeployer.deployWebModule()).

A problem with this dependency-based approach is it breaks the current "feature" whereby apps marked <distributable/> can be deployed in the default config. When this is done, the 4.x deployment code detects the absence of the cache and falls back on using the standard non-distributable session manager. That won't work if we introduce a deployment dependency.