tests: Make check-block a phony target

Fixes: b93b63f574c "test makefile overhaul"

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190319072104.32591-1-armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed