testimage.bbclass: Add dump-guest-memory cmd

testimage.bbclass: Add dump-guest-memory cmd

This command takes a set of command arguments, one of which requires
a filename so use %s which the MonitorDumper will translate to a
unique filename in the dated qmp directory.

CMD Before: {paging:false,protocol:file:%s.img}
CMD After: {paging:false,protocol:file:/yocto/poky/build/tmp/log/runtime-hostdump/qmp_00_dump-guest-memory.img}

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