python little things

1. both python2 and python3 installed on windows
   use python3:py -3 -m pip install robotframework-sshlibrary
   use python2:py -2 -m pip install robotframework-sshlibrary

2. set windows pip configure
   create a file nemed "pip.ini" in the directory(C:\Users\test\pip)
   set config information in pip.ini

3. install python lib with requirements.cfg
   pip install -r requirements.