Accept strings and lists for ssh_allow_users

[schurzi]

This makes our ssh_hardening role accept both strings and lists for ssh_allow_users.

@rndmh3ro WDYT?

Initially I thought this may be a good idea to allow more flexible use. But there is also an overlap with our documentation that states this should be a string since a long time. Also if we allow two types to be passed here we cannot use argument spec to check the variable anymore.

The alternative would be to add a type check to argument spec and simply fail before executing.

closes #838

[rndmh3ro]

It would be more flexible, yes. If we could do it in a backwards compatible way, it would be best.

Also if we allow two types to be passed here we cannot use argument spec to check the variable anymore.

We could use an assert-task for this, but I'm not really a fan.

We could also introduce a new variable ssh_allow_users_list and use this, if it exists, otherwise the string.. However this could also be complicated, e.g. what happens when both are set.

The alternative would be to add a type check to argument spec and simply fail before executing.

Can you expand on what you mean with this?