Handle GDB error in hang_analyzer.py mongodb-uniqstack module

The mongodb-uniqstack module goes through each thread and frame to detect unique or duplicate threads in a process. On the s390x platform it can error, which terminates the module, producing no backtrace output. Partial output is preferable to none, so the GDB error should be trapped and not raised.

            try:

                thread_info['frames'] = gdb.execute(arg, to_string=True).rstrip()

            except gdb.error as err:

                raise gdb.GdbError("{} {}".format(thread_info['header'], err))