Backport of Follow-up fixes to consul connect envoy command into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #16530 to be assessed for backporting due to the inclusion of the label backport/1.15.

The below text is copied from the body of the original PR.

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Description

While trying to demo #15794, I discovered some minor issues with the UX when displaying logs to a user:

• I had been checking for TLS and Plaintext ports to be < 0 (src), assuming that 0 meant a user had not set the port and it would be default. It turns out that 0 actually means gRPC is disabled and we will not get back the -1 values a user might pass as consul config.
• There is an Info log which prints to stdout, which is undesirable because -bootstrap expects the text which gets printed to stdout to be well-formatted JSON

Testing & Reproduction steps

No logical changes; mockAgent in the test has been updated to behave closer to the real agent

PR Checklist

• updated test coverage
• external facing docs updated
• not a security concern

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Overview of commits

• dc7f05b - d0adb5c - 097143b - db403de

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR