worker/migrationmaster: Add SetPlaceholderResource
worker/migrationmaster: Add SetPlaceholderResource

... to uploadWrapper. The ResourceUploader interface was extended to
include this.

reedobrien/juju,mjs/juju,marcmolla/juju,bac/juju,mikemccracken/juju,bac/juju,alesstimec/juju,ericsnowcurrently/juju,frankban/juju,waigani/juju,anastasiamac/juju,bac/juju,reedobrien/juju,marcmolla/juju,bac/juju,anastasiamac/juju,mjs/juju,mjs/juju,waigani/juju,alesstimec/juju,mikemccracken/juju,frankban/juju,anastasiamac/juju,marcmolla/juju,marcmolla/juju,anastasiamac/juju,frankban/juju,ericsnowcurrently/juju,AdamIsrael/juju,mjs/juju,anastasiamac/juju,AdamIsrael/juju,mjs/juju,waigani/juju,mjs/juju,mikemccracken/juju,alesstimec/juju,ericsnowcurrently/juju,mikemccracken/juju,waigani/juju,alesstimec/juju,ericsnowcurrently/juju,AdamIsrael/juju,alesstimec/juju,marcmolla/juju,mjs/juju,frankban/juju,reedobrien/juju,reedobrien/juju,bac/juju,ericsnowcurrently/juju,mikemccracken/juju,frankban/juju,reedobrien/juju,AdamIsrael/juju