Cert: Fail on unrecognized argument

Without that, the first argument will be passed as test name
to acts, so for example with the flag --host, it will be passed
as acts as --tc --host, and acts will complain with
`argument -tc/--testclass: expected at least one argument`
which is really misleading

Test: gd/cert/run
Tag: #gd-refactor
Change-Id: Ib020746a573f63baab80d3d4b441320d048cb75b
Signed-off-by: David Duarte <licorne@google.com>