fix(onboarding): improved connection error messages

[mrfelton]

Description:

Improved connection error messages.

This PR ports over some error handling from master that got lost in the gRPC refactor and adds some additional detail to the Failed to connect before the deadline message to help users diagnose the issue.

Error messages are not i18n aware as is the case for many errors message throughout the app - adding i18n support to the error messages can be handled separately.

Motivation and Context:

Fix #1564

How Has This Been Tested?

Try connecting with an invalid cert.

Screenshots (if appropriate):

Types of changes:

Enhancement

Checklist:

• My code follows the code style of this project.
• I have reviewed and updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes where needed.
• All new and existing tests passed.
• My commits have been squashed into a concise set of changes.

[coveralls]

Coverage decreased (-0.07%) to 20.115% when pulling 253ae63 on mrfelton:fix/1564-better-cert-errors into ed8bda5 on LN-Zap:next.

[korhaliv]

Tested ACK 253ae63