labjack: Add error handling to startup and streaming

[BrianJKoopman]

Description

This PR adds some simple error handling to the labjack agent. On initial connection failure or on stream failure, the agent will stop the twisted reactor and exit. This relies on the host manager to restart the agent in order to restart data collection.

From the log messages here we can later possibly improve the handling to not exit, but simply restart streaming. That will be easier to test with a local device.

Motivation and Context

Resolves #977.
Resolves #452.

How Has This Been Tested?

This has not been tested.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.