Update CLI for unit_test_runner.ts (#4352)

* drop server guard before unit test result check

To prevent cascading test failures when js_unit_test http server
guard is dropped before asserting that tests were successful.
This is really a band-aid and doesn't solve underlying issue with
http server.

* Update CLI for unit_test_runner.ts

* Change cli/js/tests/unit_test_runner.ts command line interface to work in 3
  modes:
  - "one-off" - run tests that match permissions of currently running
    process
  - "master" - run tests for all possible permission combinations, by
   spawning subprocesses running in "worker" mode and communicating via
   TCP socket; requires elevated permissions
  - "worker" - run tests for set of permissions provided by CLI arg;
  requires elevated permissions to setup TCP connection to "master";
  after initial setup process drops permissions to given set

* Support filtering of tests by string passed after "--" CLI arg

* Update cli/js/tests/README.md

cli/js/tests/test_util.ts

@@ -13,6 +13,7 @@ export {
   fail
 } from "../../../std/testing/asserts.ts";
 export { readLines } from "../../../std/io/bufio.ts";
+export { parse as parseArgs } from "../../../std/flags/mod.ts";
 
 export interface Permissions {
   read: boolean;