ipauser: Add support for renaming users

FreeIPA suports renaming user objects with the CLI parameter "rename",
and this parameter was missing in ansible-freeipa ipauser module.

This patch adds support for a new state 'renamed' and the 'rename'
parameter.

Tests were updated to cope with the changes.

Related to RHBZ#2234379, RHBZ#2234380

Fixes #1103