etcdmain: correctly check return values from SdNotify()

[dongsupark]

Since coreos/go-systemd@0d7fccc, SdNotify() in go-systemd started to return 2 values, sent and err. So startEtcdOrProxyV2() in etcd needs to check the 2 return values correctly. As the 2 values are independent of each other, error checking logic needs to be slightly updated too. SdNotifyNoSocket, which was previously provided by go-systemd, does not exist any more. In that case (false, nil) will be returned instead.

This was a direct reason of a travis-ci failure in fleet like this: https://travis-ci.org/coreos/fleet/builds/146093283. Although fleet has nothing to do with this API change, travis always fetches the most recent master branch for each git repo.

[heyitsanthony]

@dongsupark vendor updates need to be done through godep so the vendored packages match an upstream revision. Try running scripts/updatedep.sh with the recent go-systemd in the gopath?

[dongsupark]

@heyitsanthony Thanks. I tried to update both Godeps.json and vendor tree together, but several tests started to fail. I'm not sure why. I'll look into that tomorrow.

[heyitsanthony]

@dongsupark it looks like this is upgrading some extra deps which may be causing the failures. I think it'll be OK to keep the go-systemd updates to Godeps.json and vendor/ but keep the rest the same.

[dongsupark]

@heyitsanthony Thanks. That did the trick! :-)
Removing go-semver and clockwork from vendor, both unit tests and functional tests work without failures. Interesting.
Please have a look.

[heyitsanthony]

@dongsupark please squash the commits cmd/Godeps: update Godeps.json and cmd/vendor: update vendor trees according to go-systemd update into vendor: update go-systemd and it'll lgtm. Thanks!
/cc @xiang90

[dongsupark]

@heyitsanthony Done. Thanks!

[xiang90]

lgtm

[dongsupark]

Thanks. Now travis error from fleet is gone. :-)
BTW as for the test failure in TestServeMembersCreate, culprit seems to be a recent change in github.com/jonboulle/clockwork. I'm not sure about how to fix that, and anyway that doesn't look like a critical issue, as long as etcd doesn't update the repo in the vendor tree.