Apport info disclosure via path traversal bug in read_file

An information disclosure via path traversal was discovered in apport/hookutils.py function read_file(). This issue affects: apport 2.14.1 versions prior to 2.14.1-0ubuntu3.29+esm8; 2.20.1 versions prior to 2.20.1-0ubuntu2.30+esm2; 2.20.9 versions prior to 2.20.9-0ubuntu7.26; 2.20.11 versions prior to 2.20.11-0ubuntu27.20; 2.20.11 versions prior to 2.20.11-0ubuntu65.3;