Allow tmp dir for yml merging to be set

[kpschuck]

Currently all yml merging takes place in /tmp, but it would be nice to allow this to be set.

Another option would be to create the merged yml files with 600 permissions.

[alvid-the-bot]

Hi there!

We use Pivotal Tracker to provide visibility into what our team is working on. A story for this issue has been automatically created.

The current status is as follows:

• #147351941 Allow tmp dir for yml merging to be set

This comment, as well as the labels on the issue, will be automatically updated as the status in Tracker changes.