use 'exc_info=1' instead of import traceback

We need store traceback message in log sometime. Python logging module
already provide a argument to do that. For example, we could:

logger.error('msg', exc_info=1)
logger.debug(e, exc_info=(type_,value_,tb))
logger.exception('msg') # exception add exc_info automaticly

Change-Id: Iaf541e4f4ea139d9315ac1990f0e6079c8f8a20d
Merge "use 'exc_info=1' instead of import traceback"