e2e: add multi-node rollout test on EKS

[ptalgulk01]

Coverage so far only exercises a single node per pool, so staged rollout across a fleet has never been tested. TestMidRolloutImageChange does provision two nodes, but it runs on bink only.

TestMultiNodeRollout provisions three nodes in one pool, rolls the pool to a new image, and asserts every node boots the new digest and the pool reports all nodes updated. It declares both bink and eks; the GitHub runners cannot host three nodes, so in practice this provides coverage on EKS.

maxUnavailable is asserted inside the same polling loop that waits for convergence, so the invariant is sampled throughout the rollout. Asserting it once up front would pass trivially, as UpdatingCount is zero before the rollout starts. A violation aborts immediately instead of retrying, which would let a later poll mask it.

A node that stays Degraded past a grace period aborts the wait and reports the daemon's own error. Degraded is cleared on the next successful reconcile, so a retried transient error must not fail the test; without the early abort, a failure such as an unauthorized registry pull surfaced only as an opaque matcher timeout minutes later.

Each node's daemon pod is also checked for Running before waiting for Idle, so a pod stuck in ImagePullBackOff is named directly.