test: wait for keyring for plan apply tests (#24021)

In #23977 we merged a change to how the keyring was stored. Because keyring
initialization takes slightly longer now, this uncovered existing timing bugs in
some of our tests where tests that require the keyring (ex. plan applier tests)
were waiting for the leader but not the keyring initialization. Fix some of the
examples we've seen cause test flakes.

nomad/plan_endpoint_test.go

@@ -25,7 +25,7 @@ func TestPlanEndpoint_Submit(t *testing.T) {
 	})
 	defer cleanupS1()
 	codec := rpcClient(t, s1)
-	testutil.WaitForLeader(t, s1.RPC)
+	testutil.WaitForKeyring(t, s1.RPC, s1.Region())
 
 	// Create the register request
 	eval1 := mock.Eval()
@@ -67,7 +67,7 @@ func TestPlanEndpoint_Submit_Bad(t *testing.T) {
 	})
 	defer cleanupS1()
 	codec := rpcClient(t, s1)
-	testutil.WaitForLeader(t, s1.RPC)
+	testutil.WaitForKeyring(t, s1.RPC, s1.Region())
 
 	// Mock a valid eval being dequeued by a worker
 	eval := mock.Eval()
@@ -141,7 +141,7 @@ func TestPlanEndpoint_ApplyConcurrent(t *testing.T) {
 		c.NumSchedulers = 0
 	})
 	defer cleanupS1()
-	testutil.WaitForLeader(t, s1.RPC)
+	testutil.WaitForKeyring(t, s1.RPC, s1.Region())
 
 	plans := []*structs.Plan{}