This removes the std folder from the tree.
Various parts of the tests are pretty tightly dependent
on std (47 direct imports and 75 indirect imports, not
counting the cli tests that use them as fixtures) so I've
added std as a submodule for now.
After splitting "failFast" and "exitOnFail" arguments, there was a situation where failing tests did not exit with code 1.
* fixed argument value passed to Deno.runTests() in deno test
* fixed argument value passed to Deno.runTests() in std/testing/runner.ts
* added integration tests for deno test to ensure failFast and exitOnFail work as expected
* don't write test file to file system, but keep it in memory
