agent: rename live agent from agent.js to live.js
agent: [util] normalize prep of gateway options

- accept settings for "key" or "key file" and
load file. same for key and cert
agent: [mock] add mock agent

- simulates all behavior/events of live agent
- emits special events to faciliate logging
- refactor connect for both mock/live to use util
- live will emit/cb error if credentials are missing
test: [mock-agent] add tests for mock agent

- update agent tests to use option "key file", etc
test: [mockagent] normalize reconnect process against live