Clean up test execution flow - #14570

cc @jeremyn @J0WI @Bisaloo @cschanaj Just an FYI: I've cleaned up the tests here. Mainly, I've renamed the rules test to the validations test, and separated out test/validations.sh so that the validations test in test/run_travis.sh just calls out to that. It is now called from test.sh, so contributors will be running all the validations and not just the test coverage validation when they run ./test.sh.

I've also moved much of the testing infrastructure into tests/ and created a tests/validations/ path, where all the validation tests live. These were previously under utils/ which I thought was inappropriate since they're used mainly for tests. utils/ I consider something that, when run, creates commitable output. This is why I've retained remove-obsolete-references.sh in utils/ - it serves both purposes, but it can be run separate from the testing infrastructure.

FYI to anyone wondering: fetch-test.sh is now test/manual.sh. So instead of:

$ ./fetch-test.sh rules/Freerangekitten.com.xml

You can run:

$ test/manual.sh rules/Freerangekitten.com.xml

fetch-test.sh is still mentioned at docs/en_US/development.md#testing-and-contributing-changes-to-the-source-code.