Support puppet 3.x in om_dbspi_database provider

The withenv method has moved from Puppet::Util::Execution to
Puppet::Util. This is now correctly handled by the om_dbspi_database
provider.

For reference: The commit in the puppet repository that caused the
failures is d02169
Merge branch 'ticket/master/dbspi_fix'

* ticket/master/dbspi_fix:
  Support puppet 3.x in om_dbspi_database provider
Migrate to puppet_spec_helper

The spec dir is now a lot more cleaner and all of the special spec
handling is done by the puppetlabs_spec_helper gem