Change RexsterCluster server-host configuration

RexsterCluster now does the following when configured with
<server-host>0.0.0.0</server-host>:

1. Attempt to replace the 0.0.0.0 value with
   InetAddress.getLocalHost().getHostAddress().

2. If #1 failed, then default to "localhost"

I made this change because JGroups was attempting to send UDP
datagrams to 0.0.0.0 (and failing).
Add JChannel hostname logging

Most importantly, this commit prevents
HintedRexsterClient#openConnection(String) from silently swallowing
exceptions and returning.  Now exceptions during openConnection are
logged at the warn level.  Null is still returned.
Gracefully handle nulls in RexPro response msgs

I was getting NullPointerExceptions off the statement
"msg.Results.get()" for some queries issued through
HintedRexsterClient.  This commit replaces the NPE with returning an
empty results list.