Merge pull request #636 from letsencrypt/mktemp

make mktemp in integration tests work on OS X

tests/integration/_common.sh

@@ -2,7 +2,9 @@
 
 if [ "xxx$root" = "xxx" ];
 then
-    root="$(mktemp -d)"
+    # The -t is required on OS X. It provides a template file path for
+    # the kernel to use.
+    root="$(mktemp -d -t leitXXXX)"
     echo "Root integration tests directory: $root"
 fi
 store_flags="--config-dir $root/conf --work-dir $root/work"