Add "Serializable" to some classes (#194)

[itmustbesid]

During app development using the Azure Java SDK, certain errors were not handled
properly, causing NotSerializable exceptions. This changes adds the interface
marker to appropriate classes.

[jianghaolu]

@itmustbesid How are you serializing them? We serialize some of these types upon every request through Jackson and it has been working for us.

[itmustbesid]

Our setup is a little complex -- we are using a remoting service between two tomcat instances: when the 'client' makes an API call involving the Azure SDK, that request is sent to the 'server'. From what I can tell, the 'server' encounters a CloudError and tries to send that response back to the 'client' ... at this point, we see the error:

org.springframework.remoting.RemoteAccessException: Could not access HTTP invoker remote service at [https://127.0.0.2:8443/dt-remote-invoker/remoting/RemotingService]; nested exception is java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: com.microsoft.azure.CloudError
at org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.convertHttpInvokerAccessException(HttpInvokerClientInterceptor.java:216) ~[spring-web-4.2.9.RELEASE.jar:4.2.9.RELEASE]
at org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.invoke(HttpInvokerClientInterceptor.java:147) ~[spring-web-4.2.9.RELEASE.jar:4.2.9.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.2.9.RELEASE.jar:4.2.9.RELEASE]
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:208) ~[spring-aop-4.2.9.RELEASE.jar:4.2.9.RELEASE]
at com.sun.proxy.$Proxy353.invoke(Unknown Source) ~[?:?]
at com.desktone.vmgr.client.VirtualizationManagerClient$RemoteHttpProxyProvider$1.invoke(VirtualizationManagerClient.java:358) ~[dt-vmgr-api-17.2.0.jar:?]

Caused by: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: com.microsoft.azure.CloudError
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1539) ~[?:1.8.0_131]

Caused by: java.io.NotSerializableException: com.microsoft.azure.CloudError
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184) ~[?:1.8.0_131]

[itmustbesid]

@jianghaolu I wondered if you had any more thoughts about this issue and the corresponding pull request? I know it's bad practice to "push" ones own pull requests, but our project manager is hoping this issue can be addressed soon. Many thanks!