Use fatal library in path_srv, cert_srv and sciond

[sustrik]

This patch also moves logging the fatal condition into the failing
goroutine and makes servers wait for 1 second before exiting. This
way we can collect multiple fatal errors in the log in case the
first one is not the most informative one.

---

This change is 

[lukedirtwalker]

Reviewed 6 of 6 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[lukedirtwalker]

Reviewed 8 of 8 files at r2.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @sustrik)

---

go/godispatcher/main.go, line 61 at r2 (raw file):

	<-fatal.Chan()
	// Prometheus encountered a fatal error, thus we exit.
	log.Crit("Unable to listen and serve")

Those two lines above are no longer needed.

---

go/lib/fatal/fatal.go, line 15 at r2 (raw file):

provide

provides

---

go/lib/fatal/fatal.go, line 19 at r2 (raw file):

they

not needed

---

go/lib/fatal/fatal.go, line 59 at r2 (raw file):

	// Ask main goroutine to shut down the application.
	select {
	case fatalC <- struct{}{}:

TIL that works a on a nil channel.

---

go/lib/fatal/fatal.go, line 62 at r2 (raw file):

		// Block until the application shuts down.
		select {}
	case <-time.After(10 * time.Second):

10 is plenty, maybe use 5 or 2?

[sustrik]

Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @lukedirtwalker)

---

go/godispatcher/main.go, line 61 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

Those two lines above are no longer needed.

Done.

---

go/lib/fatal/fatal.go, line 15 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

provide

provides

Done.

---

go/lib/fatal/fatal.go, line 19 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

they

not needed

Done.

---

go/lib/fatal/fatal.go, line 62 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

10 is plenty, maybe use 5 or 2?

Done.

[lukedirtwalker]

Reviewed 2 of 2 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved