Improve command line executors error messages.

- Improve descriptions of command line arguments.
- Remove meaningless default arguments.
- Add more checks to make sure command line arguments are sane.
- Add more information to some error messages.

Bug: 21161902
Change-Id: I509db5933b117b4313b6a7836274ffe091cca9d0
diff --git a/executor/xeLocalTcpIpLink.cpp b/executor/xeLocalTcpIpLink.cpp
index 0550582..8bc9491 100644
--- a/executor/xeLocalTcpIpLink.cpp
+++ b/executor/xeLocalTcpIpLink.cpp
@@ -62,7 +62,7 @@
 		deProcess_destroy(m_process);
 		m_process = DE_NULL;
 
-		XE_FAIL((std::string("Failed to start server: ") + err).c_str());
+		XE_FAIL((std::string("Failed to start ExecServer '") + execServerPath + "' : " + err).c_str());
 	}
 
 	try