Improves unsupported Cloud Foundry service message

[#37]
This message is specific to Cloud Foundry.  Making a more generic
handling of this error will require a more substantial rewrite.

src/Steeltoe.Tooling/Drivers/CloudFoundry/CloudFoundryDriver.cs

@@ -99,7 +99,12 @@ namespace Steeltoe.Tooling.Drivers.CloudFoundry
         public void DeployService(string service)
         {
             var svcInfo = _context.Configuration.GetServiceInfo(service);
-            var cfServiceDef = _context.Target.Configuration.ServiceTypeProperties[svcInfo.ServiceType];
+            _context.Target.Configuration.ServiceTypeProperties.TryGetValue(svcInfo.ServiceType, out var cfServiceDef);
+            if (cfServiceDef == null)
+            {
+                throw new ToolingException($"No Cloud Foundry service available for '{svcInfo.Service}' [{svcInfo.ServiceType}]");
+            }
+
             var cfCmd = $"create-service {cfServiceDef["service"]} {cfServiceDef["plan"]} {service}";
             var svcArgs = _context.Configuration.GetServiceArgs(service, "cloud-foundry") ?? "";
             if (svcArgs.Length > 0)

test/Steeltoe.Tooling.Test/Drivers/CloudFoundry/CloudFoundryDriverTest.cs

@@ -135,6 +135,15 @@ namespace Steeltoe.Tooling.Test.Drivers.CloudFoundry
             Shell.LastCommand.ShouldBe("cf create-service p-redis shared-vm my-service");
         }
 
+        [Fact]
+        public void TestDeployUnavailableService()
+        {
+            Context.Configuration.AddService("my-service", "zipkin");
+            var e = Assert.Throws<ToolingException>(
+                () => _driver.DeployService("my-service")
+            );
+            e.Message.ShouldBe("No Cloud Foundry service available for 'my-service' [zipkin]");
+        }
 
         [Fact]
         public void TestUndeployService()