Warning about tox not working in Vagrant setup

Adds a warning to the vagrant setup section of the devstack setup
documentation. The warning states that tox will not be able to run
if the user sets up shared folders. It also provides instructions
on disabling shared folders.

Change-Id: I776004da8ab86760eaeaef7957c9bfba111d2f36

devstack/barbican-vagrant/Vagrantfile

@@ -14,6 +14,8 @@ Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
   config.vm.network "forwarded_port", guest: 5000, host: 5000
 
   config.vm.provision "shell", path: "install_devstack.sh"
+
+  # Create Synced Folder
   config.vm.synced_folder "./devstack", "/opt/stack", create: true
 
   config.vm.provider "virtualbox" do |v|
@@ -21,4 +23,4 @@ Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
     v.memory = 2048
     v.cpus = 2
   end
-end
+end

doc/source/setup/devstack.rst

@@ -25,6 +25,14 @@ To simplify the setup process of running Barbican on DevStack, there is a
 Vagrantfile that will automatically setup up a VM containing Barbican
 running on Devstack.
 
+.. warning::
+
+    Upon following these steps, you will not be able to use tox tools
+    if you setup a shared folder. This is because making hard-links is
+    required, but not permitted if the project is in a shared folder.
+    If you wish to use tox, comment out the `Create Synced Folder`
+    section in `barbican/devstack/barbican-vagrant/Vagrantfile`.
+
 1. Obtain Barbican vagrant file
    If you don't already have the file then clone the repo below