Windows10 で Vagrant が起動しない場合の対処方法

$ vagrant -v
Vagrant 1.8.1

$ vagrant up
==>  Provider 'virtualbox' not found. We'll automatically install it now...
     The installation process will start below. Human interaction may be
     required at some points. If you're uncomfortable with automatically
     installing this provider, you can safely Ctrl-C this process and install
     it manually.
==>  Downloading VirtualBox 5.0.10...
     This may not be the latest version of VirtualBox, but it is a version
     that is known to work well. Over time, we'll update the version that
     is installed.

==>  Installing VirtualBox. This will take a few minutes...
     A couple pop-ups will occur during this installation process to
     ask for admin privileges as well as to install Oracle drivers.
     Please say yes to both. If you're uncomfortable with this, please
     install VirtualBox manually.
==>  VirtualBox has successfully been installed!
No usable default provider could be found for your system.

Vagrant relies on interactions with 3rd party systems, known as
"providers", to provide Vagrant with resources to run development
environments. Examples are VirtualBox, VMware, Hyper-V.

The easiest solution to this message is to install VirtualBox, which
is available for free on all major platforms.

If you believe you already have a provider available, make sure it
is properly installed and configured. You can see more details about
why a particular provider isn't working by forcing usage with
`vagrant up --provider=PROVIDER`, which should give you a more specific
error message for that particular provider.