First pass at making using the java cookbook optional.

First pass at making using the java cookbook optional.

For #84.
On a separate note, this should access attributes consistently; that is, use either symbols or strings, but not both.

The cookbook seems to prefer symbols, so this would be more consistently written as:

```ruby
if node[:zookeeper][:use_java_cookbook] == true
  node.override[:'build-essential'][:compile_time] = true
```