Remove need to explicitly set VAGRANT_HOME before running tests (#1580)

Ensure that the tests always set VAGRANT_HOME into the environment to
prevent the global plugin manager from trying to load the plugins under
this directory.

spec/spec_helper.rb

@@ -38,13 +38,12 @@ rescue LoadError
   end
 end
 
-
-require 'vagrant-libvirt'
-require 'vagrant-spec/unit'
-
-Dir[File.dirname(__FILE__) + '/support/**/*.rb'].each { |f| require f }
-
 RSpec.configure do |config|
+  # set VAGRANT_HOME before any thing that requires vagrant is loaded to prevent
+  # the global plugin manager from trying to use the default VAGRANT_HOME.
+  temp_dir = Dir.mktmpdir("rspec-")
+  ENV['VAGRANT_HOME'] = temp_dir
+
   # ensure that setting of LIBVIRT_DEFAULT_URI in the environment is not picked
   # up directly by tests, instead they must set as needed. Some build envs will
   # may have it set to 'qemu:///session'.
@@ -52,6 +51,10 @@ RSpec.configure do |config|
     ENV.delete('LIBVIRT_DEFAULT_URI')
   end
 
+  config.after(:suite) do
+    FileUtils.remove_entry temp_dir
+  end
+
   config.mock_with :rspec do |mocks|
     mocks.verify_partial_doubles = true
   end
@@ -59,3 +62,7 @@ RSpec.configure do |config|
   # don't run acceptance tests by default
   config.filter_run_excluding :acceptance => true
 end
+
+require 'vagrant-spec/unit'
+
+Dir[File.dirname(__FILE__) + '/support/**/*.rb'].each { |f| require f }

spec/unit/plugin_spec.rb

@@ -3,6 +3,7 @@
 require 'spec_helper'
 require 'support/sharedcontext'
 
+require 'vagrant-libvirt'
 require 'vagrant-libvirt/plugin'