Only require installs when giving arguments on vagrant.

Both the automated version and non-automated version were
giving their respective plugin installation messages even
when just typing `vagrant`.

vagrant/base/analyticstack/Vagrantfile

 Vagrant.require_version ">= 1.8.7"
-require_relative '../../.vagrantplugins'
-install_plugins(['vagrant-vbguest'])
+
+unless ARGV.empty?
+  require_relative '../../../vagrantplugins'
+  install_plugins(['vagrant-vbguest'])
+end
 
 VAGRANTFILE_API_VERSION = "2"
 

vagrant/base/devstack/Vagrantfile

 Vagrant.require_version ">= 1.8.7"
-require_relative '../../.vagrantplugins'
-install_plugins(['vagrant-vbguest'])
+
+unless ARGV.empty?
+  require_relative '../../../vagrantplugins'
+  install_plugins(['vagrant-vbguest'])
+end
 
 VAGRANTFILE_API_VERSION = "2"
 

vagrant/release/analyticstack/Vagrantfile

 Vagrant.require_version ">= 1.8.7"
-require_relative '../../.vagrantplugins'
-install_plugins(['vagrant-vbguest'])
+
+unless ARGV.empty?
+  require_relative '../../../vagrantplugins'
+  install_plugins(['vagrant-vbguest'])
+end
 
 VAGRANTFILE_API_VERSION = "2"
 

vagrant/release/devstack/Vagrantfile

 Vagrant.require_version ">= 1.8.7"
-require_relative '../../.vagrantplugins'
-install_plugins(['vagrant-vbguest'])
+
+unless ARGV.empty?
+  require_relative '../../../vagrantplugins'
+  install_plugins(['vagrant-vbguest'])
+end
 
 VAGRANTFILE_API_VERSION = "2"