Allow nova client state to create keypairs

- Added a state `keypair_present` that ensures that a keypair with
  a given name is present
- Extended nova/client.sls to call the `keypair_present` state if
  keypairs are defined in metadata

Related PROD: PROD-12876

Change-Id: I928b4e75759069cd0214013688ce82709ad0232e
3 files changed