This changes all the puppet 3 validate_* functions
to use the validate_legacy function.
The validate_legacy function has been available since
about three years but require Puppet >= 4.4.0 and since
there is Puppet 4.10.12 as latest we should assume people
are running a fairly new Puppet 4 version.
This is the first step to then remove all validate function
calls and use proper types for parameter as described in spec .
A recent change making nova-metadata-api work with wsgi  moved
the vendordata plugin parameters to the nova::metadata manifest.
While this is conceptually correct as nova-metadata is the one that
should be using this parameters. In practice the parameters are also
used in compute drivers (in the ironic driver, for instance), thats
why we should split them to be able to deploy nova-metadata-api
separate from nova-compute.