Do not fail service containers without the healthcheck

src/Runner.Worker/ContainerOperationProvider.cs

@@ -110,7 +110,7 @@ namespace GitHub.Runner.Worker
             {
                 var healthcheck = await ContainerHealthcheck(executionContext, container);
 
-                if (!string.Equals(healthcheck, "healthy", StringComparison.OrdinalIgnoreCase))
+                if (!(string.Equals(healthcheck, "healthy", StringComparison.OrdinalIgnoreCase) || string.IsNullOrEmpty(healthcheck)))
                 {
                     unhealthyContainers.Add(container);
                 }

src/Test/L0/Worker/ContainerOperationProviderL0.cs

@@ -23,6 +23,7 @@ namespace GitHub.Runner.Common.Tests.Worker
         private Mock<IJobServerQueue> serverQueue;
         private Mock<IPagingLogger> pagingLogger;
         private List<string> healthyDockerStatus = new List<string> { "healthy" };
+        private List<string> emptyDockerStatus = new List<string> { string.Empty };
         private List<string> unhealthyDockerStatus = new List<string> { "unhealthy" };
         private List<string> dockerLogs = new List<string> { "log1", "log2", "log3" };
 
@@ -81,6 +82,23 @@ namespace GitHub.Runner.Common.Tests.Worker
 
         }
 
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public async void RunServiceContainersHealthcheck_healthyServiceContainerWithoutHealthcheck_AssertSucceededTask()
+        {
+            //Arrange
+            Setup();
+            _dockerManager.Setup(x => x.DockerInspect(_ec.Object, It.IsAny<string>(), It.IsAny<string>())).Returns(Task.FromResult(emptyDockerStatus));
+
+            //Act
+            await containerOperationProvider.RunContainersHealthcheck(_ec.Object, containers);
+
+            //Assert
+            Assert.Equal(TaskResult.Succeeded, _ec.Object.Result ?? TaskResult.Succeeded);
+
+        }
+
         private void Setup([CallerMemberName] string testName = "")
         {
             containers.Add(new ContainerInfo() { ContainerImage = "ubuntu:16.04" });