[TEST] fix explain API rest test that assumes there is only a single

node in the cluster (incorrect assumption)

rest-api-spec/src/main/resources/rest-api-spec/test/cluster.allocation_explain/10_basic.yaml

@@ -19,9 +19,6 @@
       cluster.state:
         metric: [ master_node ]
 
-    # This relies on there only being a single node in the test cluster, which
-    # is currently true, but if this changes in the future this test will need
-    # to be changed
   - do:
       cluster.allocation_explain:
         body: { "index": "test", "shard": 0, "primary": true }
@@ -31,10 +28,10 @@
   - match: { index: "test" }
   - match: { shard: 0 }
   - match: { primary: true }
-  - match: { can_remain_on_current_node: "yes" }
-  - match: { can_rebalance_cluster: "no" }
-  - match: { can_rebalance_to_other_node: "no" }
-  - match: { rebalance_explanation: "rebalancing is not allowed" }
+  - is_true: can_remain_on_current_node
+  - is_true: can_rebalance_cluster
+  - is_true: can_rebalance_to_other_node
+  - is_true: rebalance_explanation
 
 ---
 "cluster shard allocation explanation test with empty request":