The command executed in ValidateController function uses the
image name of the running container. This is a problem in multiarch
images, since the image name is the name of the image specific to
the architecture, but the image passed as parameter is the multiarch
one (as the test are architecture agnostic), making the test to fail.

This patch fixes it by making the logic use a command that get the
multiarch name given in the container spec.
Signed-off-by: Miguel Herranz <miguel@midokura.com>