Set TMPDIR to /var/tmp by default
Set TMPDIR to /var/tmp by default

We have had some issues with users squashing large images or pulling large
content from github, that could trigger crashes based on the size of /tmp.

Docker had an issue with this back in 2016. https://github.com/golang/go/issues/14021

The discussion there was to change the default to /var/tmp.

This change will only effect systems that do not set the TMPDIR environment variable.

Signed-off-by: Daniel J Walsh <7800de746fd39599bc46177380ea6aede7e31e16@redhat.com>

TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,nalind/buildah,projectatomic/buildah,nalind/buildah-1,rhatdan/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,projectatomic/buildah,nalind/buildah,rhatdan/buildah,rhatdan/buildah,nalind/buildah-1,nalind/buildah-1