Infra: Error out if initial sciond connect fails

[oncilla]

Currently, infraenv.NewRouter returns a router with a nil sciond
connection, if every attempt fails to connect to sciond.

This happens because the err variable is shadowed, and thus never
set in the outer scope.

---

This change is 

[scrye]

Reviewed 1 of 1 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

---

go/lib/infra/infraenv/infraenv.go, line 309 at r1 (raw file):

		sciondConn, err := sciond.NewService(sd.Path, true).Connect()
		if err == nil {
			router = &snet.BaseRouter{

What do you think about simplifying this further, to something like:

// NewRouter constructs a path router for paths starting from localIA.
func NewRouter(localIA addr.IA, sd env.SciondClient) (snet.Router, error) {
        ticker := time.NewTicker(time.Second)
        timer := time.NewTimer(sd.InitialConnectPeriod.Duration)
        defer ticker.Stop()
        defer timer.Stop()
        // XXX(roosd): Initial retrying is implemented here temporarily.
        // In https://github.com/scionproto/scion/issues/1974 this will be
        // done transparently and pushed to snet.NewNetwork.
        for {
                sciondConn, err := sciond.NewService(sd.Path, true).Connect()
                if err != nil {
                        select {
                        case <-ticker.C:
                        case <-timer.C:
                                return nil, common.NewBasicError("Timed out during initial sciond connect", err)
                        }
                } else {
                        return &snet.BaseRouter{
                                IA: localIA,
                                PathResolver: pathmgr.New(
                                        sciondConn,
                                        pathmgr.Timers{
                                                NormalRefire: time.Minute,
                                                ErrorRefire:  3 * time.Second,
                                        },
                                        log.Root(),
                                ),
                        }, nil
                }
        }
}