Don't use non-1.8.5-compatible methods 'Object#tap' and 'Dir.mktmpdir'

These methods aren't available until Ruby 1.8.6 (Dir.mktmpdir) and Ruby 1.8.7
(Object#tap).

Reviewed-By: Jacob Helwig <jacob@puppetlabs.com>
(cherry picked from commit 61df3f7c39d74b82e37f48c3519293406036e1e9)