Fix the usage of mktemp on Mac OS
Fix the usage of mktemp on Mac OS

The version of mktemp on Mac OS is not compatible with versions on
linux distributions. It requires either a template or a template prefix.

This change will supply a template prefix if running the plain mktemp fails
while executing the subdir tests.

http://unix.stackexchange.com/questions/30091/fix-or-alternative-for-mktemp-in-os-x

Vhex/spf-tools,jsarenik/spf-tools