testimage: Add testimage_dump_target to kwargs

This passes the list of commands to run on the OEQemuTarget when
the TargetDumper needs to run in a test context due to a failure
on the target.

This is added here as a kwargs because the 'd' dictionary is not
available in the staticmethod getTarget in the
OERuntimeTestContextExecutor class. The OEQemuTarget is different
from the QemuTarget which already uses the list of commands from
testimage_dump_target from 'd'. The create_dir() is needed to
initialize the TargetDumper's dump_dir variable.

Signed-off-by: Saul Wold <saul.wold@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>