Support modifying sudoers Defaults

[deric]

This PR introduces a possibility to modify sudoers defaults without the need to provide whole configuration file.

However, it would be only possible to add new entries:

sudo::defaults:
  mailto: 
    value: 'root'

would be converted to a line in /etc/sudoers

Defaults mailto=root

The sudoers syntax is fairly complex:

     Default_Type ::= 'Defaults' |
                      'Defaults' '@' Host_List |
                      'Defaults' ':' User_List |
                      'Defaults' '!' Cmnd_List |
                      'Defaults' '>' Runas_List

     Default_Entry ::= Default_Type Parameter_List

     Parameter_List ::= Parameter |
                        Parameter ',' Parameter_List

     Parameter ::= Parameter '=' Value |
                   Parameter '+=' Value |
                   Parameter '-=' Value |
                   '!'* Parameter

There's a possibility to add more complex configurations:

sudo::defaults:
  mailto:
    type: '@hosts_list'
    operator: '+='
    value: some@email.com

[bschonec]

What a great idea. You just saved me a lot of time, too in implementing this. I'm going to play with your changes today.

[deric]

Ruby 2.5 is EOL, probably could be updated to Ruby 2.6, right?

Ruby 2.5 status: eol release date: 2017-12-25 EOL date: 2021-04-05

[bschonec]

@deric Would you be so kind as to slipstream my updates to your fork and resubmit this pull request?

[saz]

@deric LGTM but I'd prefer, to have separate PRs for using hiera and the defaults part. Easier to spot any issues in each part.

[deric]

@bschonec I've added your RHEL7 template modifications. @saz I understand the PR is modifying too many files. I've added a common Ruby function that formats the defaults config. Thus each OS template requires only single line change.

[saz]

Thanks for this PR. I'll do some more changes and will get a new release published asap.