Added dfu._read to handle abstracted device specifications. Modified write commands to utilize _read.
Added dfu._read to handle abstracted device specifications. Modified write commands to utilize _read.

spark/particle-cli,kennethlimcp/particle-cli,spark/particle-cli,spark/particle-cli,spark/particle-cli,spark/particle-cli,kennethlimcp/particle-cli,kennethlimcp/particle-cli,kennethlimcp/particle-cli,spark/particle-cli,kennethlimcp/particle-cli,kennethlimcp/particle-cli