test/cmd: Make some "ut dm" tests only available on sandbox

Currently, the "dm" suite in unit tests (ut) is only available on
sandbox. Make sure that all cmd tests that are part of this suite are
only available on sandbox and not attempted to be run on hardware (where
it will fail to be able to be started).

Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
1 file changed