Various additions to cli for idempotency

Includes:

- ignore uuid 
  - allows to ignore uuid of director in the manifest

- skip-if-exists for release
  - allows `bosh upload release` to be idempotent

- skip-if-exists for stemcell
  - allows `bosh upload stemcell` to be idempotent

- update-if-exists for micro
  - allows `bosh micro` to be idempotent