Allow configuration of CERN Virtual Machine

Add module to manage the configuration files for the CERN Virtual
Machine.  The configuration files are placed in /etc/cernvm.  Should
only be applied on CernVMs.  Account for unique location of java
executable on the cernvm in condor configuration.  Configurable options
are the version of cvmfs to use, whether CernVM should acts as batch
node, desktop, etc., what experiment the cernvm should be set up for,
which cvmfs repositories will be made avaiable, and where to place the
configuration files.

Changes:
   * new file:   cernvm/manifests/init.pp
   * new file:   cernvm/templates/site.conf.erb
   * modified:   condor/manifests/client.pp
   * modified:   condor/templates/condor_config.local.csnode.erb
   * modified:   gce_node/manifests/init.pp