test: test update for Go 1.12.5 and related changes

Update to Go 1.12.5 testing. Remove deprecated unused and gosimple
pacakges, and mask staticcheck 1006. Also, fix unconvert errors related
to unnecessary type conversions and following staticcheck errors:
- remove redundant return statements
- use for range instead of for select
- use time.Since instead of time.Now().Sub
- omit comparison to bool constant
- replace T.Fatal and T.Fatalf in tests with T.Error and T.Fatalf respectively because the goroutine calls T.Fatal must be called in the same goroutine as the test
- fix error strings that should not be capitalized
- use sort.Strings(...) instead of sort.Sort(sort.StringSlice(...))
- use he status code of Canceled instead of grpc.ErrClientConnClosing which is deprecated
- use use status.Errorf instead of grpc.Errorf which is deprecated

Related #10528 #10438

tests/e2e/ctl_v3_auth_test.go

@@ -859,7 +859,7 @@ func authTestWatch(cx ctlCtx) {
 			defer close(donec)
 			for j := range puts {
 				if err := ctlV3Put(cx, puts[j].key, puts[j].val, ""); err != nil {
-					cx.t.Fatalf("watchTest #%d-%d: ctlV3Put error (%v)", i, j, err)
+					cx.t.Errorf("watchTest #%d-%d: ctlV3Put error (%v)", i, j, err)
 				}
 			}
 		}(i, tt.puts)

tests/e2e/ctl_v3_watch_no_cov_test.go

@@ -133,7 +133,7 @@ func watchTest(cx ctlCtx) {
 		go func(i int, puts []kv) {
 			for j := range puts {
 				if err := ctlV3Put(cx, puts[j].key, puts[j].val, ""); err != nil {
-					cx.t.Fatalf("watchTest #%d-%d: ctlV3Put error (%v)", i, j, err)
+					cx.t.Errorf("watchTest #%d-%d: ctlV3Put error (%v)", i, j, err)
 				}
 			}
 			close(donec)

tests/e2e/etcd_release_upgrade_test.go

@@ -168,7 +168,7 @@ func TestReleaseUpgradeWithRestart(t *testing.T) {
 			epc.procs[i].Config().execPath = binDir + "/etcd"
 			epc.procs[i].Config().keepDataDir = true
 			if err := epc.procs[i].Restart(); err != nil {
-				t.Fatalf("error restarting etcd process (%v)", err)
+				t.Errorf("error restarting etcd process (%v)", err)
 			}
 			wg.Done()
 		}(i)