Fix sciond logging for processing path replies.

[kormat]

• The logger does not expect an error after the string, so removing
  nil.
• The logger does not do a good job with []error, so created
  common.FmtErrors to handle this.

Before:

2019-08-21 09:01:33.830842+0000 [WARN] Failed to verify reply debug_id=747f80c4 trace_id=64dc60702aa9bf7 LOG15_ERROR="Key(<nil>) is not a string: <nil>" LOG15_ERROR="Key([]error) is not a string: [Failed to verify seg seg="55c11074ec66 2019-08-21 09:01:31+0000 1-ff00:0:110 1>41 1-ff00:0:111"
    DEBUGTHISTHING 2 Failed to verify seg seg="55c11074ec66 2019-08-21 09:01:31+0000 1-ff00:0:110 1>41 1-ff00:0:111"
    DEBUGTHISTHING 2]" LOG15_ERROR="Normalized odd number of arguments by adding nil"

After:

2019-08-20 15:59:05.693430+0000 [WARN] Failed to verify reply debug_id=e544675c trace_id=6963201a9432fbae errors=
>  Failed to verify seg seg="55c11074ec66 2019-08-20 15:59:01+0000 1-ff00:0:110 1>41 1-ff00:0:111"
>      DEBUGTHISTHING 2
>  Failed to verify seg seg="55c11074ec66 2019-08-20 15:59:01+0000 1-ff00:0:110 1>41 1-ff00:0:111"
>      DEBUGTHISTHING 2

---

This change is 

[lukedirtwalker]

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @kormat)

---

go/lib/common/errors.go, line 189 at r1 (raw file):

// FmtErrors formats a slice of errors for logging.
func FmtErrors(es []error) string {
	s := make([]string, 0)

make([]string, 0, len(es))

[kormat]

Reviewable status: 1 of 2 files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker)

---

go/lib/common/errors.go, line 189 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

make([]string, 0, len(es))

Done. ish.

[lukedirtwalker]

Reviewed 1 of 1 files at r2, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

[lukedirtwalker]

Reviewable status: complete! all files reviewed, all discussions resolved