Clearer warning message when connecting a non-secure HBase client to a secure HBase server

When a connection from a non secure-rpc-engine
client is attempted the warning message you get is related to version
mismatch:

Mar 28, 3:27:13 PM WARN org.apache.hadoop.ipc.SecureServer Incorrect
header or version mismatch from 172.29.82.121:43849 got version 3
expected version 4

While this is true, it isn't as useful as it could be. A more specific error message warning end users that they're connecting with a non-secure client may be more useful.