Use custom chef install URL to resolve Ubuntu dpkg lock issue

Issue is reported in chef/bento#609
Using custom chef URL instead of default one (https://www.chef.io/chef/install.sh)
we are able to skip the error "dpkg: error: dpkg status database is locked by another process"

Signed-off-by: Luca Carrogu <carrogu@amazon.com>

.kitchen.cloud.yml

@@ -16,6 +16,8 @@ driver_config:
 provisioner:
   name: chef_zero
   require_chef_omnibus: 14.2.0
+  # use custom chef install URL to cope with issue https://github.com/chef/bento/issues/609
+  chef_omnibus_url: https://raw.githubusercontent.com/aws/aws-parallelcluster-cookbook/develop/util/chef-install.sh
   retry_on_exit_code:
     - 35 # 35 is the exit code signaling that the node is rebooting
   max_retries: 1