add SignAndSave to Alert_tests

This adds the nessesary code to create src/test/data/alertTests.raw with signed alerts required for these tests. Somebody with an alert key (ping @langerhans) has to follow the steps outlined in the code to create a valid alertTests.raw.

Note that the alertnotify test doesn't pass. It's receiving all seven generated alerts but only expects to be alerted to four of them.