New Filter: debug-kit

This Filter processes any VM definition which has a `debug-kit` key:

    ---
    vms:

      - name: pe-323-master
        debug-kit: true
        ...

When activated, the filter parses the `name` and uses the information
contained therein to configure a `pe_bootstrap` provisioner for the VM.
The filter sets default values for the VM `hostname` and the `role`, `version`
and `master` configuration values of the `pe_boostrap` provisioner. Any
existing values for these attributes that have been set directly in the VM
definition or inherited from a role will be left intact by the filter.
Add preliminary support for nightly versions

This commit extends the `debug-kit` filter to parse VM names such as
`pe-33nightly-master` in addition to `pe-323-master`. The numeric portion of
the version, `33`, is extracted into a `release` that can be substituted into a
PEBuild `download_root`.
Add example VMs for PE 3.3.0
Log a warning if Oscar is not installed

If Oscar is not loaded, the entire Vagrantfile is a no-op. The most common
cause for this is that the plugin is not installed. Log a warning to let the
user know why they are not seeing any VMs.

Fixes Sharpie/puppet-debugging-kit#2.