[k8s] Default Service protocol to "TCP" (Azure#2929)

If you create a module with Docker createOptions like so:
```json
{
  "ExposedPorts":{
    "35000":{}
  },
  "HostConfig":{
    "PortBindings":{
      "35000":[{"HostPort":"35000"}]
    }
  }
}
```

The Docker API will default the port to be "TCP".  Therefore, the Docker->K8s translation should do the same.

edge-agent/src/Microsoft.Azure.Devices.Edge.Agent.Kubernetes/edgedeployment/service/PortAndProtocol.cs

@@ -7,6 +7,9 @@ namespace Microsoft.Azure.Devices.Edge.Agent.Kubernetes.EdgeDeployment.Service
 
     public class PortAndProtocol
     {
+        static Option<PortAndProtocol> empty = Option.None<PortAndProtocol>();
+        static string defaultProtocol = "TCP";
+
         public int Port { get; }
 
         public string Protocol { get; }
@@ -21,18 +24,28 @@ public static Option<PortAndProtocol> Parse(string name)
         {
             if (string.IsNullOrWhiteSpace(name))
             {
-                return Option.None<PortAndProtocol>();
+                return empty;
             }
 
             string[] portProtocol = name.Split('/', StringSplitOptions.RemoveEmptyEntries);
-            if (portProtocol.Length != 2)
+            if (portProtocol.Length > 2)
+            {
+                return empty;
+            }
+
+            if (!int.TryParse(portProtocol[0], out int port))
             {
-                return Option.None<PortAndProtocol>();
+                return empty;
             }
 
-            if (!int.TryParse(portProtocol[0], out int port) || !SupportedProtocols.TryGetValue(portProtocol[1], out string protocol))
+            // Docker defaults to TCP if not specified.
+            string protocol = defaultProtocol;
+            if (portProtocol.Length > 1)
             {
-                return Option.None<PortAndProtocol>();
+                if (!SupportedProtocols.TryGetValue(portProtocol[1], out protocol))
+                {
+                    return empty;
+                }
             }
 
             return Option.Some(new PortAndProtocol(port, protocol));

edge-agent/test/Microsoft.Azure.Devices.Edge.Agent.Kubernetes.Test/PortAndProtocolTest.cs

@@ -31,11 +31,28 @@ public void UnableToParseUnsupportedProtocol()
         [Fact]
         public void UnableToParseInvalidPort()
         {
-            var result = PortAndProtocol.Parse("1a23/HTTP");
+            var result = PortAndProtocol.Parse("1a23/TCP");
 
             Assert.Equal(Option.None<PortAndProtocol>(), result);
         }
 
+        [Fact]
+        public void UnableToParseTooManyParts()
+        {
+            var result = PortAndProtocol.Parse("10/tcp/udp");
+
+            Assert.Equal(Option.None<PortAndProtocol>(), result);
+        }
+
+        [Fact]
+        public void DefaultProtocolIsTCP()
+        {
+            var result = PortAndProtocol.Parse("3434").OrDefault();
+
+            Assert.Equal(3434, result.Port);
+            Assert.Equal("TCP", result.Protocol);
+        }
+
         [Theory]
         [InlineData("123/TCP", 123, "TCP")]
         [InlineData("456/UDP", 456, "UDP")]