Vagrantfile: Add support for CentOS 7

Add support for CentOS 7 Vagrant VMs. This also updates the bindep.txt
file so it can be easier to copy it across OSA repositories.

Change-Id: Iaf2ef0a0d6278605ce411da0c55d3c667e77a588

Vagrantfile

@@ -22,4 +22,13 @@ Vagrant.configure(2) do |config|
     SHELL
   end
 
+  config.vm.define "centos7" do |centos7|
+    centos7.vm.box = "centos/7"
+    centos7.vm.provision "shell", inline: <<-SHELL
+      sudo su -
+      cd /vagrant
+      ./run_tests.sh
+    SHELL
+  end
+
 end

bindep.txt

@@ -9,6 +9,18 @@
 # is better to have this file empty, otherwise OpenStack-CI
 # will fall back to installing its default packages which
 # will potentially be detrimental to the tests executed.
+#
+# Note:
+# This file is maintained in the openstack-ansible-tests repository.
+# https://git.openstack.org/cgit/openstack/openstack-ansible-tests/tree/bindep.txt
+# If you need to remove or add extra dependencies, you should modify
+# the central file instead and once your change is accepted then update
+# this file as well. The purpose of this file is to ensure that Python and
+# Ansible have all their necessary binary requirements on the test host before
+# tox executes. Any binary requirements needed by services/roles should be
+# installed by those roles in their applicable package install tasks, not through
+# using this file.
+#
 
 # Base requirements for Ubuntu
 build-essential   [platform:dpkg]