Fix unicode() issue for Python3 compatibility

Controllers in API code used unicode() function which is not supported in Python3.
In order to be compatible with python2.x and python3.x unicode() function is
replaced by six.text_type() function.

Change-Id: I98c7e566dba5befbfa794f9a7aa04301295b5ae2
Closes-Bug:  #1257929
Merge "Fix unicode() issue for Python3 compatibility"