Prefix catch all error responses to make message recognizable

Summary:
It is currently hard to detect whether a test failed because of a legitimate
error by a developer or because something is going wrong in selendroid
internals. This diff marks error responses from the server that indicate
something has gone wrong in the internals of selendroid.

Test Plan:
```
$ mvn clean install
...
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] selendroid ......................................... SUCCESS [  0.105 s]
[INFO] android-driver-app ................................. SUCCESS [  2.107 s]
[INFO] selendroid-server-common ........................... SUCCESS [  0.890 s]
[INFO] selendroid-server .................................. SUCCESS [ 16.272 s]
[INFO] selendroid-grid-plugin ............................. SUCCESS [  0.826 s]
[INFO] selendroid-common .................................. SUCCESS [  0.968 s]
[INFO] selendroid-standalone .............................. SUCCESS [ 15.209 s]
[INFO] selendroid-client .................................. SUCCESS [  0.564 s]
[INFO] selendroid-test-app ................................ SUCCESS [  4.431 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
```

Reviewers: mkonicek

Reviewed By: mkonicek

Differential Revision: https://reviews.facebook.net/D28929