Rename local_ansible_data_path to java_download_dir

[John Freeman]

The variable name local_ansible_data_path is potentially confusing as it's actually a path on the remote machine (from the Ansible perspective); also, given this is a java role the variable should be prefixed with java_.

It's still beneficial to support a common variable for where to store downloads so java_download_dir will default to x_ansible_download_dir if set.

Renaming the variable to java_download_dir will be clearer and less misleading.