Add wrapper functions to test_common.sh
Add wrapper functions to test_common.sh

Add xsed which provides a generic way to call GNU sed in tests.
Add make_temp_dir and make_temp_file which provide a platform agnostic
way to create temporary files.

OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap