providers/virtualbox: check VBOX_MSI_INSTALL_PATH on Win [GH-3852]

CHANGELOG.md

@@ -26,6 +26,8 @@ BUG FIXES:
       `docker stop`. [GH-3798]
   - providers/docker: Better error messaging when SSH is not ready
       direct to container. [GH-3763]
+  - providers/virtualbox: On Windows, check `VBOX_MSI_INSTALL_PATH`
+      for VBoxManage path as well. [GH-3852]
   - provisioners/puppet: Fix setting facter vars with Windows
       guests. [GH-3776]
   - guests/darwin: Respect mount options for NFS. [GH-3791]

plugins/providers/virtualbox/driver/base.rb

@@ -30,9 +30,10 @@ module VagrantPlugins
 
             # On Windows, we use the VBOX_INSTALL_PATH environmental
             # variable to find VBoxManage.
-            if ENV.has_key?("VBOX_INSTALL_PATH")
+            if ENV.has_key?("VBOX_INSTALL_PATH") ||
+              ENV.has_key?("VBOX_MSI_INSTALL_PATH")
               # Get the path.
-              path = ENV["VBOX_INSTALL_PATH"]
+              path = ENV["VBOX_INSTALL_PATH"] || ENV["VBOX_MSI_INSTALL_PATH"]
               @logger.debug("VBOX_INSTALL_PATH value: #{path}")
 
               # There can actually be multiple paths in here, so we need to