`vagrant box update` should print the used version

Example without this patch:

$ vagrant box update
==> default: Checking for updates to 'berendt/opensuse-13.1-x86_64'
    default: Version constraints:
    default: Provider: virtualbox
==> default: Box 'berendt/opensuse-13.1-x86_64' (v0.2.0) is running the latest version.

Example with this patch:

$ vagrant box update
==> default: Checking for updates to 'berendt/opensuse-13.1-x86_64'
    default: Version constraints: 0.2.0
    default: Provider: virtualbox
==> default: Box 'berendt/opensuse-13.1-x86_64' (v0.2.0) is running the latest version.