Restore original order of agent startup functions

[dereknola]

Proposed Changes

• Partial revert of Allow executors to define containerd and cridockerd behavior #9184, restoring the orginal order of setting up container runtimes, closing the channel, then running the kubelet.
• Renamed AgentReady to ContainerRuntimeReady to better reflect what the channel is actually tracking.
• Closed E2E coverage gap around this issue by increasing number of etcd nodes in the split role test.

Types of Changes

Bugfix

Verification

Manually running split servers (3 etcd, 2 cp, 1 agent), the cluster now initialized all etcd nodes correctly.

Testing

Change is now covered by E2E test, and the docker/drone test stage now covers this case.

Linked Issues

#9540

User-Facing Change

Further Comments

I will not be squashing this, as we want the revert commit to stand alone from the other 2 "new" changes.

[brandond]

Would you mind also pulling in brandond@1af2fe4

I think that should work?

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (1c17461) 49.50% compared to head (466decb) 42.95%.

Files	Patch %	Lines
pkg/agent/run.go	41.66%	4 Missing and 3 partials ⚠️
pkg/etcd/etcd.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9539      +/-   ##
==========================================
- Coverage   49.50%   42.95%   -6.56%     
==========================================
  Files         151      154       +3     
  Lines       13475    13523      +48     
==========================================
- Hits         6671     5809     -862     
- Misses       5464     6548    +1084     
+ Partials     1340     1166     -174     

Flag	Coverage Δ
e2etests	?
inttests	39.52% <52.38%> (+0.01%)	⬆️
unittests	15.96% <16.66%> (?)

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