Cache PersistenceProviders within the same deployment

See wildfly-dev ml discussion http://lists.jboss.org/pipermail/wildfly-dev/2014-September/002984.html about calls to PersistenceProviderResolver.getPersistenceProviders() should return a cached list. The cache should be per deployment.

We can probably reuse our PersistenceProviderResolverImpl.persistenceProviderPerClassLoader map, just need to be careful that addDeploymentSpecificPersistenceProvider() is called early before any calls to getPersistenceProviders().