Merge branch 'glarizza-bug/3.0.x/12833_fix_salt' into 3.0.x

• glarizza-bug/3.0.x/12833_fix_salt: Update Documentation to YARD standard Update spec tests Clean up comments Create base64_decode_string Provide wrapper method for new StringIO objects Do not fail if ShadowHashData doesn't exist Wrap user plist retrieval into get_users_plist() Wrap ShadowHashData setting into its own method Optimize calls for operating system version