yocto/oeqa: Add check argument to DomUTest.run_cmd

BspTest.run_cmd contains a 'check' argument which, if True,
automatically checks the status code of the call and fails the test if
non-zero.

DomUTest.run_cmd overrides the above, but does not currently accept a
'check' argument, meaning that an error is thrown if a bsp test attempts
to set this argument explicitly. Additionally, this override needs to
validate the status code if check is True.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>