* Close #198
* All details in that issue
* Solution based upon:
  - https://github.com/saltstack-formulas/vault-formula/pull/35#issuecomment-509854411

This fixes a change introduced by 634deac where createhome was changed from True to False (by default).

This change honnor the default "global default" "users.createhome" from defaults.sls

using `|json` would let the state get an error if gid is a string, as it would
not be converted.

Using directly the `None` yaml value, and letting numbers as string be
converted by yaml parser.

members, addusers, delusers, and in pillar examples

Also remove warning for passing unknown arguments on group.absent

To get it to work with RHEL7 with salt 2018.x

The former is deprecated since Carbon.

Since https://github.com/saltstack-formulas/users-formula/pull/182 the
home directory was created by salt which prevent "adduser" behavior to
copy /etc/skel in newly created directory.

Ensure the parent directory of the home dir is existing instead.

Fixes #181

The state will not fail gracefully, instead you will get
an error like this one:

          ID: users_rhertzog_user_gitconfig_0
    Function: git.config_set
        Name: alias.br
      Result: False
     Comment: State 'git.config_set' was not found in SLS 'users'
              Reason: 'git' __virtual__ returned False
     Changes:

And since pillar data can't be (easily) tuned according to minion's
status, we really need this check here.

My tests with Salt 2017.7.3 have shown that cmd.has_exec() is reliable
for this, contrary the what the comment was implying.

Fixing my previous change which errors in a particular scenario.

Error: Conflicting ID 'users_ssh_auth_source_username_0' when keys are added and removed simultaneously.

Fixing the conflict and sending a new pull request

Fixes #118
Duplicate of #120

Fixes: 150

* add ability to configure prime_group without gid

If the user to be created is a system user, it makes no sense to create
him a primary group which is not a system group too.