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.

If a primary group is set on the user, and a authorized_keys is provied in ssh_auth_file, the formula fails. This solves that by using the user_group set earlier in the formula

Unreasonable values for 'expire' (after 9999-12-31
on Linux, before 1975-01-01 on *BSD) get divided
by 86400 (number of seconds in a day) when too big
or multiplied by 86400 when too small.

Tested on CentOS 6 (Salt 2015.5.5) and FreeBSD 10.2
(Salt 2015.8.0) with following values:

  - 24854 (2038-01-18 in days since epoch)
  - 157766400 (1975-01-01 00:00:00 UTC in seconds since epoch)
  - 3313526400 (2075-01-01 00:00:00 UTC in seconds since epoch)
  - 16000 (2013-10-22 in days since epoch)
  - 18000 (2019-04-14 in days since epoch)

(Sponsored by av.tu-berlin.de and fokus.fraunhofer.de)