- Add an environment variale option, RSPEC_DESTROY.
  When set to 'no' or 'false' this prevents the VM from being
  destroy before and after a test.
Merge branch 'override_destroy'

Conflicts:
	lib/rspec-system/node_set.rb
	lib/rspec-system/node_set/base.rb
	lib/rspec-system/node_set/vagrant.rb
	lib/rspec-system/node_set/vsphere.rb
	lib/rspec-system/spec_helper.rb