clients: add dig

Change-Id: I78822e9d68b36973362f0790f3c2f6e676cc6b94
ci: Enable coverage report and allow unit test output in XML format

Change-Id: I952654aa25d2bdfb5ba1885d1c7570cfdb7e3edf
ci: Enable Travis CI

Change-Id: I0b87242535ddc0443eea56ff349817aeae1117ff
tools/ndns-daemon: fix bug that validator cannot fetch certificate

refs #2206

Change-Id: I10c69d95e6a5fd020038211ce419763fd62afcb3