Using common method 'bool_from_string' from oslo strutils

Using common method 'bool_from_string' from oslo strutils to replace
utils.string_to_bool.

partially implements blueprint common-client-library-2

Change-Id: I101eb89174ac229aa1025bc4aea8b1c0c5594705
Merge "Using common method 'bool_from_string' from oslo strutils"