test: properly clean up temp directory
test: properly clean up temp directory

A persistent failure on OS X 10.11 uncovered a inproperly cleaned up
temp directory in this test. This changes the mkdirSync call to clean up
properly in case it throws.

PR-URL: https://github.com/nodejs/io.js/pull/2164
Reviewed-By: Evan Lucas <ad0310dc5270cefb6ee6879263270aed9b1e9982@me.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node