Application crashes if any DNS name cannot be resolved

[fchavant]

Expected behavior

DNS names from differents domains/TLDs are used for seeds nodes in config/*/config.json to improve reliability. If one or a few of them cannot be resolved (DNS entry missing, resolver returning an error, TLD issue, etc.) the application still functions (especially if the peers table is populated).

Actual behavior

Application crashes if even a single DNS name cannot be resolved. A message similar to the following is logged:
2018-12-05 10:07:13 224: Failed to resolve peer domain name testnet-seed-05.will-not-resolve.io to an IP address

Steps to reproduce

• apply the following patch:

--- a/config.json       2018-12-05 10:20:24.029725152 +0000
+++ b/config.json       2018-12-05 10:20:13.049767544 +0000
@@ -23,7 +23,7 @@
                                "wsPort": 7001
                        },
                        {
-                               "ip": "testnet-seed-05.lisk.io",
+                               "ip": "testnet-seed-05.will-not-resolve.io",
                                "wsPort": 7001
                        }
                ]

• try to start the application with LISK_NETWORK=testnet

Which version(s) does this affect? (Environment, OS, etc...)

Core >=1.2.0