test: Fix flaky tests by really waiting for manager readiness #3064

Job	Run time
setup	20s
e2e-experimental (logs)	3m 36s
e2e-self-mon (logs, healthy)	3m 50s
e2e-experimental (metrics)	4m 5s
e2e-self-mon (logs, backpressure)	3m 31s
e2e-istio	3m 58s
e2e (logs)	3m 40s
e2e-experimental (traces)	3m 19s
e2e-self-mon (logs, outage)	3m 48s
e2e (metrics && set_a)	3m 39s
e2e-self-mon (metrics, healthy)	3m 34s
e2e (metrics && set_b)	3m 28s
e2e-self-mon (metrics, backpressure)	3m 30s
e2e-self-mon (metrics, outage)	3m 16s
e2e (traces)	3m 27s
e2e-self-mon (traces, healthy)	3m 17s
e2e (telemetry)	3m 30s
e2e-self-mon (traces, backpressure)	3m 15s
e2e (max-pipeline)	3m 14s
e2e (telemetry-log-analysis)	4m 10s
e2e-self-mon (traces, outage)	3m 38s
	1h 12m 5s

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