Add attribute for cassandra tmp directory

[JackBracken]

I'm working on a custom RHEL image that as part of a set of security policies has the noexec flag set for the /tmp partition. Cassandra needs to execute some of its temporary files in order to boot successfully.

This pull request adds an attribute node['cassandra']['tmp_dir'], and updates the config recipe to create this directory if it does not exist and if the attribute is set.

More details from datastax.

[JackBracken]

Looks like the last build timed out on bundle install, closed and reopened to force another build.

[michaelklishin]

Thank you!