This patch adds support for streaming a raw image directly onto the disk,
that means no more time spent writing the image to a tmpfs partition prior
to copying it to the disk. Checksum computation is also done as the image
is being streamed. Streaming raw images is disabled by default, however
this behavior can be enabled by passing a key called "stream_raw_images"
with the value of True to the prepare_image() command of IPA.
For non-raw images this may not be possible, not sure about all image
file formats, but common types such as qcow2 requires random access to
the image file in order to be converted to raw.
Closes-Bug: #1505685
Change-Id: Iddf67907bc9b54bbd3065a97064cb5a3602cfe18
e320bb8942