Improve VBox kernel module detection for Gentoo [GH-710]

CHANGELOG.md

@@ -43,6 +43,8 @@ IMPROVEMENTS / BUG FIXES:
   - Improve the SSH "ready?" check by more gracefully handling timeouts. [GH-841]
   - Human friendly error if connection times out for HTTP downloads. [GH-849]
   - Detect when the VirtualBox installation is incomplete and error. [GH-846]
+  - Detect when kernel modules for VirtualBox need to be installed on Gentoo
+    systems and report a user-friendly error. [GH-710]
   - All `vagrant` commands that can take a target VM name can take one even
     if you're not in a multi-VM environment. [GH-894]
   - Hostname is set before networks are setup to avoid very slow `sudo`

plugins/providers/virtualbox/driver/meta.rb

@@ -121,7 +121,8 @@ module VagrantPlugins
           # Note: We split this into multiple lines because apparently "".split("_")
           # is [], so we have to check for an empty array in between.
           output = execute("--version")
-          if output =~ /vboxdrv kernel module is not loaded/
+          if output =~ /vboxdrv kernel module is not loaded/ ||
+            output =~ /VirtualBox kernel modules are not loaded/i
             raise Vagrant::Errors::VirtualBoxKernelModuleNotLoaded
           elsif output =~ /Please install/
             # Check for installation incomplete warnings, for example: