Fix proxy usage for docker external

The process that retrieves Docker images hosted externally was
missing a step in its configuration. This change fix the
configuration and unblock the pending Unit Tests.

Change-Id: I5a6b39086eb806bab5bb2667092a154e230d33ef
Signed-off-by: Victor Morales <victor.morales@intel.com>
Issue-ID: INT-227
diff --git a/bootstrap/vagrant-onap/Vagrantfile b/bootstrap/vagrant-onap/Vagrantfile
index c10cb0b..dc8b347 100644
--- a/bootstrap/vagrant-onap/Vagrantfile
+++ b/bootstrap/vagrant-onap/Vagrantfile
@@ -290,6 +290,7 @@
       config.proxy.http     = ENV['http_proxy']
       config.proxy.https    = ENV['https_proxy']
       config.proxy.no_proxy = ENV['no_proxy']
+      configuration['socks_proxy'] = ENV['socks_proxy']
     end
 
     if Vagrant.has_plugin?('vagrant-vbguest')