[FileSystem] Improve assert and add Terminate in unit test.

Speculative fix for the Xcode bots where we were seeing the assertion
being triggered because we would re-initialize the FileSystem without
terminating it.

llvm-svn: 345849

lldb/unittests/ScriptInterpreter/Python/PythonTestSuite.cpp

@@ -38,4 +38,6 @@ void PythonTestSuite::TearDown() {
   PyGILState_Release(m_gil_state);
 
   ScriptInterpreterPython::Terminate();
+  HostInfoBase::Terminate();
+  FileSystem::Terminate();
 }