Unicorn: create tmpdir for Ruby, as it is picky

Create a TMPDIR for Ruby / Workhorse, as Rails is picky about the qualifications of the directory provided by Dir.tmpdir

Effectively: must be not world writable, or sticky.

Here, we're making it both Sticky and non-world writable (3770)

We'll fix this in the process-wrappers in the CNGs, and this can then be removed from the chart itself.

Closes #1651 (closed)

cc @nolith