Initial bigip_node version
bigip_node: additional code

- checks if address already assigned to other node name
- add description for node
- check for node addres changes
- add missing code "node exists, potentially modify attributes"
Documentation additions and major refactor
Fixed version_added and removed reference to traceback module
Merge pull request #4712 from mhite/bigip_node

New BIG-IP module for managing node objects