meta-webos: webos.inc: use MACHINE subdirectory in DEPLOY_DIR_IMAGE

:Release Notes:
Use MACHINE subdirectory in DEPLOY_DIR_IMAGE like newer oe-core does.

:Detailed Notes:
With shared BUILD directory it's even more important to distinguish
which file belongs to which MACHINE in DEPLOY_DIR_IMAGE.

:Testing Performed:
Only build tested.

:Build Notes:
Requires to be applied together with:
https://gpro.palm.com/54907
https://gpro.palm.com/54909
https://g2g.palm.com/6192

:QA Notes:
No change to image.

:Issues Addressed:
[ES-346] Use the same BUILD directory for all MACHINEs

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I11743da12f622e55c483a67a2421d6ced6c5ccb7
Originally-Reviewed-on: https://gpro.palm.com/54908
Reviewed-on: https://g2g.palm.com/6335
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>