Fixed an issue using password-based authentication with Capistrano.
Removed a debug statement for the vSphere provider.
Terminate the initial_ssh_user connection when we're done with it.
Added a way to retrieve the OS version for an instance.
Added a way of specifying packages to be installed by OS version.
Omit the @os_version and @capistrano ivars when converting an InstanceItem to a hash.
Support fetching the OS version even when Capistrano is unavailable, if we can.
Make sure instance items have a handle to the Capistrano reference immediately after creation.

Previously the association was only made after booting Capistrano.  This meant running rubber:create followed by rubber:bootstrap worked fine, but broke uber tasks such as rubber:create_staging.
Worked around an issue with Ubuntu 14.04 on VMware.