On systems with dash as /bin/sh there were failures while invoking ddimage.
Fix to let it work with both bash and dash shells.
[YOCTO #4617]
(From OE-Core master rev: 4c6f7a5d8bd6ada434b91037ecd5db06f3eac814)
(From OE-Core rev: 6f3dd6cfff781a7ab1c0495982da5c723e894ca9)
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>