Add debug info for failed RTT test
Add debug info for failed RTT test

The test TestConnzRTT() failed once with "invalid duration". Adding
the original string in case of error to understand better.

Signed-off-by: Ivan Kozlovic <a15f8b81a160b4eebe5c84e9e3b65c87b9b2f18e@synadia.com>

wallyqs/gnatsd,wallyqs/gnatsd,apcera/gnatsd,nats-io/gnatsd,nats-io/gnatsd,apcera/gnatsd