Fix libxslt-dev reference

The libxslt package on Ubuntu is actually named libxslt1-dev, but it
provised the libxslt-dev package.  This means that each time puppet
runs, it looks for, doesn't find and reinstalls libxslt-dev, which
actually installs libxslt1-dev.

Change-Id: Ibd21d70605ab98a569e7abae654d0463672b7b37