Skip ThreadStateTestCase.test_state_after_continue_with_dwarf on Darwin

Summary:
- This test cause Python crash randomly on darwin builder
- Tracked by bug 'llvm.org/pr23669'

Test Plan: ./dotest.py -m --executable /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/lldb --framework /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/LLDB.framework -A x86_64 -C clang -p TestThreadStates.py

Reviewers: chaoren, vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D10053

llvm-svn: 238495