cloudinit: export AddBootTextFile

This will be needed by the Joyent provider.
provider/joyent: add a static route for the internal network

Fixes LP #1401130.
Merge pull request #1317 from mjs/1401130-joyent-routing

provider/joyent: add a static route for the internal network

Fixes LP #1401130

No unit tests yet because it appears the local/fake Joyent API doesn't save machine metadata. I'll fix this and add a test in a later PR. 

This change works in a real environment though.

(Review request: http://reviews.vapour.ws/r/633/)