dns srv resolution with IP addresses seems to fail on reverse lookup

Scenario: starting in 1.5.7, with an SRV record that contains only IP addresses that do not reverse lookup into hostnames, we try to resolve the address. That causes bootstrap failure. From the output at the time of failure, it looks like it causes a failure to bootstrap normally, and then the client actually tries localhost.

From the logs here:

{"level":"ERROR","when":"2018-05-31 13:30:23,866","method":"c.c.c.c.u.ConnectionString","thread":"localhost-startStop-1","msg":"Unable to resolve address hostname.redacted.com:0"}

Related to JVMCBC-513.