Refactor check.py so that groups of tests can be split into separate … (

WebAssembly#849)

* Refactor check.py so that groups of tests can be split into separate files

- Move helper util functions into test/shared.py
- Move scripts/support.py to test/support.py
- Split s2wasm tests into its own file

* Fix flake8 warnings for shared.py and s2wasm.py

* Move test scripts from test/ to scripts/test/

* Replace 'from shared import *' with explicit imports

.travis.yml

@@ -39,7 +39,7 @@ install:
 
 before_script:
   # Check the style of a subset of Python code until the other code is updated.
-  - flake8 ./scripts/*
+  - flake8 ./scripts/
 
 script:
   - ./check.py --only-prepare

auto_update_tests.py

@@ -2,7 +2,7 @@
 
 import os, sys, subprocess, difflib
 
-from scripts.support import run_command, split_wast
+from scripts.test.support import run_command, split_wast
 
 print '[ processing and updating testcases... ]\n'