ubuntu16.04: Add libxml2-dev dependency

Not sure what changed, but Torque requires libxml2-dev and it
wasn't being installed on ubunutu 16.04, so list it in the
always installed dependencies.

Signed-off-by: Brian Barrett <[email protected]>

Author: bwbarrett

attributes/default.rb

@@ -108,7 +108,7 @@
                                               tcl-dev automake autoconf python-parted libtool librrd-dev libapr1-dev libconfuse-dev
                                               apache2 libboost-dev libdb-dev tcsh libssl-dev  libncurses5-dev libpam0g-dev libxt-dev
                                               libmotif-dev libxmu-dev libxft-dev libhwloc-dev man-db lvm2 libmpich-dev libopenmpi-dev
-                                              r-base libatlas-dev libblas-dev libfftw3-dev libffi-dev libssl-dev) 
+                                              r-base libatlas-dev libblas-dev libfftw3-dev libffi-dev libssl-dev libxml2-dev) 
   default['cfncluster']['kernel_devel_pkg']['name'] = "linux-image-extra"
   default['cfncluster']['kernel_devel_pkg']['version'] = node['kernel']['release']
   default['cfncluster']['ganglia']['apache_user'] = 'www-data'