* added mtu state and command node to interfaces
* added mtu state and command node to bonds
* added admin_down to interfaces
* [cumulus_switch] Implemented admin_down on interfaces
* [cumulus_switch] Implemented new MTU nodes
* Added iterator key feature
* [cumulus_switch] Fixed bond deletion bug
* [cumulus_switch] When all of a bond's slave interfaces are re-assigned, that bond is now deleted automatically instead of being converted to an interface
* Fixed a bug where fabrics were being inherited in reverse order
* Primitive node documentation
* Added ability to set custom plugin options
* [cumulus_switch] Fixed a few bond creation edge-case bugs
* Upgraded paramiko to 2.4.2 to eliminate CVE-2018-1000805 vulnerability