CC Bridge component to enable Diego to upload files to Cloud Controller's blobstore

Uploading droplets & build artifacts via CC involves crafting a correctly-formed multipart request. For Droplets we also poll until the async job completes.

To specify a remote cloud controller to test against, use the following environment variables:

CC_ADDRESS the hostname for a deployed CC CC_USERNAME, CC_PASSWORD the basic auth credentials for the droplet upload endpoint CC_APPGUID a valid app guid on that deployed CC

####Learn more about Diego and its components at diego-design-notes