Check plugin name with version spec in has_plugin

If one passes a version spec to `Vagrant.has_plugin?`, the actual plugin name is ignored and any installed plugin which matches the version spec makes the check pass. Fix this by also checking for plugin name match in addition to the requested version spec.

lib/vagrant.rb

@@ -156,7 +156,7 @@ module Vagrant
     Plugin::Manager.instance.installed_specs.any? do |s|
       match = s.name == name
       next match if !version
-      next version.satisfied_by?(s.version)
+      next match && version.satisfied_by?(s.version)
     end
   end