Add remote tests

Include tests for remote template file and remote source image.
Correct key names in design
Update setup_mounts documentation comment

Signed-off-by: William Douglas <william.douglas@intel.com>
Add working source image download

Currently staging files in '/', may change to be specified in conf or
move to '/tmp/'.

Signed-off-by: William Douglas <william.douglas@intel.com>
Add tests for handling remote image installation

Signed-off-by: William Douglas <william.douglas@intel.com>