Disable nacl_tls_unittest under Valgrind.
Disable nacl_tls_unittest under Valgrind.

BUG=none
TEST=one failure less in "... buildbot=tsan-trusted tsan_bot_tests"
Review URL: http://codereview.chromium.org/7071043

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@5495 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client