Allow storing input from user in a pause prompt

It came up a few times in #ansible today that there are some situations where you might want to capture the users input inline (one example was confirming that a user did indeed want to delete a database, or other destructive operations). This simply sets the user_input var in the result dict that allows you to use register on a pause to use it down the road for something else.

//cc @drybjed @candeira