adds os_tuning_params to the vagrant_variables.yml.sample file

When using virtualbox with vagrant the default set of os_tuning_params
was locking up my vms. Specifically the vm.vfs_cache_pressure setting.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>

vagrant_variables.yml.sample

@@ -35,3 +35,7 @@ vagrant_box: ubuntu/trusty64
 
 # use vagrant_storagectl: 'SATA Controller' for CentOS
 vagrant_storagectl: 'SATAController'
+
+os_tuning_params:
+  - { name: kernel.pid_max, value: 4194303 }
+  - { name: fs.file-max, value: 26234859 }