Hardware managers should load at runtime. This will ensure the agent is
ready to respond to API calls before it begins heartbeating. Also, it
means in case of a syntax or other error in a HardwareManager, the agent
will crash before it heartbeats, which is better than it working until a
hardware manager method is needed.
Change-Id: I9403ce7bedc8d5af20b6d84371367253b26b74c2
Closes-bug: 1490008