Temporarily install apachebench on wtp1004

Gabriel is using it for benchmarking to determine how many Parsoid
machines to buy.

I installed this by hand on March 1st, but Leslie told me to puppetize
it anyway, so here goes. Once it's no longer needed, we'll change this
to ensure=>absent.

Change-Id: I96d30802b7bcce52637689d13f8fecf5be89b2cc