Changing module name to match the standard

Every other puppetlabs openstack module uses the naming scheme "puppetlabs-X", and other modules expect this one to use this scheme as well:

Warning: Missing dependency 'puppetlabs-cinder':
  'puppetlabs-nova' (v1.0.1) requires 'puppetlabs-cinder' (>= 1.0.1)
  'puppetlabs-openstack' (v1.0.3) requires 'puppetlabs-cinder' (>= 1.0.1)
Merge pull request #21 from comptonqc/patch-1

Changing module name to match the standard