Remove StackTrace from EventSource Message

[eerhardt]

Proposed Changes

When logging connection exception information to the EventSoruce we are putting the full exception ToString in the Message which clutters it to the users.

Instead, just put the Exception.Message in the EventSource event message. The full exception information comes in the details of the EventSource event.

Fix #1493

Types of Changes

What types of changes does your code introduce to this project?
Put an x in the boxes that apply

• Bug fix (non-breaking change which fixes issue HandleMainLoopException puts exception StackTrace in the EventSource Message #1493)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

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• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

cc @lukebakken

[lukebakken]

Thank you!