Add exos_facts module. Known limitations at this time include:
- Interface MTU is not reported.
- Only primary interface IP is reported.
Add basic unit tests for the exos_facts module.
An EXOS CLI prompt can be prefixed with '! ' (shutting down), '* '
(running configuration does not match saved configuration), and
can include various status tokens within parentheses after these
prefixes. Update prompt regex to accept valid CLI prompts.
