fix(k8s-nemesis): make flush_and_reshard run only having 14+ cores

Operator's racy bug [1] gets reproduced on slow backends and
nodes with small number of cores.
So, skip it for the nodes that are not running on the EKS and have
less than 14 cores.

[1] scylladb/scylla-operator#1077

sdcm/nemesis.py

@@ -1273,7 +1273,10 @@ def disrupt_nodetool_flush_and_reshard_on_kubernetes(self):
         """Covers https://github.com/scylladb/scylla-operator/issues/894"""
         if not self._is_it_on_kubernetes():
             raise UnsupportedNemesis('It is supported only on kubernetes')
-        if self.cluster.params.get('cluster_backend') == "k8s-gke":
+        if self.cluster.params.get('cluster_backend') != "k8s-eks" or self.cluster.nodes[0].scylla_shards < 14:
+            # NOTE: bug https://github.com/scylladb/scylla-operator/issues/1077 reproduces better
+            #       on slower machines with smaller amount number of cores.
+            #       So, allow it to run only on fast K8S-EKS backend having at least 14 cores per pod.
             raise UnsupportedNemesis(
                 "Skipped due to the following bug: "
                 "https://github.com/scylladb/scylla-operator/issues/1077")