Reduce failures to connect from fatal errors to warnings

[metalicjames]

Follow up from #168. This PR reduces all failures to connect from fatal errors to warnings. This should eliminate the startup order requirement of the system components.

I think I got them all, but it's possible I missed one.

[wadagso-gertjaap]

Without this the 2PC system cannot start up regardless of the order:

The 2PC sentinel creates separate network clients for each of the other sentinels (for the attestation feature) - meaning if connecting to it fails, the sentinel fails to start up.

Combined with the fact that the sentinel doesn't start listening before it has connected to other sentinels means the system can't ever start up.

[HalosGhost]

utACK. There are a couple of now-misleading comments that need to be updated.

[HalosGhost]

Thank you for fixing those comments. This looks like a really simple change that both closes out the issue introduced by #135 and has a nice improvement in eliminating the not-particularly-well-documented component startup-order requirement.

Looks great to me.

[kylecrawshaw]

Thanks for changing this @metalicjames . This fixes the issues I observed in #167