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: I23924db3000feadcfe823c6cc979ea9752a13fa9
Merge "Using common method 'bool_from_string' from oslo strutils"