serial:1 only gathers facts from one host at a time

[jpea...@sparkpost.com]

I have a playbook that I need to execute serially on a set of hosts, but 2.1 no longer gathers facts from all of the matching hosts and only gathers the current host.  For example, this breaks templates that require facts from all of the hosts (e.g. ansible_default_ipv4).  This works fine with 1.9.4.

Workaround is to add an additional play on the set of hosts.  I presume this was an "enhancement" but at the very least needs to be documented (with the workaround).

John