Follow symlinks in test/mjsunit to allow linked test directories.

Wasm mjsunit tests aren't being detected when symlinked into
test/mjsunit/wasm. This causes symlinked directories in that
directory to be included.

BUG=None
TEST=local
R=dehrenberg@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1332463002

Cr-Commit-Position: refs/heads/master@{#30600}

test/mjsunit/testcfg.py

@@ -45,7 +45,7 @@ class MjsunitTestSuite(testsuite.TestSuite):
 
   def ListTests(self, context):
     tests = []
-    for dirname, dirs, files in os.walk(self.root):
+    for dirname, dirs, files in os.walk(self.root, followlinks=True):
       for dotted in [x for x in dirs if x.startswith('.')]:
         dirs.remove(dotted)
       dirs.sort()