Update and select seboolean rules for R67

[yuumasato]

Description:

• Fix description of sebool_deny_execmem, and warning about possible
  issues.
• Add rationale to rules the SELinux booleans.

Rationale:

• Supports ANSSI R67

[yuumasato]

@openscap-ci test this please

[JAORMX]

 Please, check if the contents below are correctly expanded:
Source yaml: /content/linux_os/guide/system/selinux/selinux-booleans/sebool_deny_execmem/rule.yml 

[yuumasato]

@JAORMX Thanks, that issue is fixed.
Now the build fails only in the rhel7 node, :/

Exception while handling file: /home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/build/rhel7/rules/sebool_deny_execmem.yml
Traceback (most recent call last):
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/utils/gen_tables.py", line 93, in <module>
    result = output_class_map[args.output_type](args.product, args.build_dir).get_result()
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/utils/gen_tables.py", line 48, in __init__
    rule = ssg.build_yaml.Rule.from_yaml(r_file)
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/ssg/build_yaml.py", line 1087, in from_yaml
    yaml_contents = open_and_macro_expand(yaml_file, env_yaml)
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/ssg/yaml.py", line 102, in open_and_macro_expand
    return open_and_expand(yaml_file, substitutions_dict)
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/ssg/yaml.py", line 85, in open_and_expand
    yaml_contents = _open_yaml(expanded_template, yaml_file, substitutions_dict)
  File "/home/jenkins/workspace/scap-security-guide-pull-requests/label/rhel7/ssg/yaml.py", line 70, in _open_yaml
    raise e
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:python/unicode'
  in "<unicode string>", line 36, column 23