IMGAPI-447: clarify check errors on AddImageFileFromSource endpoint
IMGAPI-447: clarify check errors on AddImageFileFromSource endpoint

numericillustration/sdc-imgapi,joyent/sdc-imgapi,joyent/sdc-imgapi,numericillustration/sdc-imgapi,numericillustration/sdc-imgapi,joyent/sdc-imgapi