tests: @screenshot must accept **kwargs
tests: @screenshot must accept **kwargs

If the decorated function has keywords arguments, @screenshot will
fail because it does not have a **kwargs argument. It must be accepted
and passed to the wrapped function unmodified.

conorsch/securedrop,garrettr/securedrop,garrettr/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,micahflee/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,garrettr/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,micahflee/securedrop,heartsucker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,micahflee/securedrop,conorsch/securedrop