cmd/coordinator: fix gomote ssh connection closing

gomote ssh connections immediately close with a "Connection closed"
error. The coordinator logs indicate an error in our call to pty.Start,
which is used to relay the tty between ssh connections. When the
coordinator was updated to Go 1.16 from Go 1.13 in July, it likely
caused this issue (see creack/pty#96).

Fixes golang/go#48329

Change-Id: Ieec5d2220c6c5ef4c53de594acbdd598a1bafb6d
Reviewed-on: https://go-review.googlesource.com/c/build/+/349092
Trust: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

cmd/coordinator/remote.go

@@ -34,8 +34,8 @@ import (
 	"time"
 	"unsafe"
 
+	"github.com/creack/pty"
 	"github.com/gliderlabs/ssh"
-	"github.com/kr/pty"
 	"golang.org/x/build/buildlet"
 	"golang.org/x/build/dashboard"
 	"golang.org/x/build/internal/coordinator/pool"

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/aws/aws-sdk-go v1.30.15
 	github.com/bradfitz/go-smtpd v0.0.0-20170404230938-deb6d6237625
 	github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f
+	github.com/creack/pty v1.1.15
 	github.com/davecgh/go-spew v1.1.1
 	github.com/gliderlabs/ssh v0.3.3
 	github.com/golang/protobuf v1.4.3
@@ -25,7 +26,6 @@ require (
 	github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7
 	github.com/jackc/pgx/v4 v4.13.0
 	github.com/jellevandenhooff/dkim v0.0.0-20150330215556-f50fe3d243e1
-	github.com/kr/pty v1.1.8
 	github.com/tarm/serial v0.0.0-20180830185346-98f6abe2eb07
 	go.opencensus.io v0.23.0
 	go4.org v0.0.0-20180809161055-417644f6feb5

go.sum

@@ -106,8 +106,9 @@ github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f h1:JOrtw2xFKzlg+
 github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/coreos/pkg v0.0.0-20160727233714-3ac0863d7acf/go.mod h1:E3G3o1h8I7cfcXa63jLwjI0eiQQMgzzUDFVpN/nH/eA=
 github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d/go.mod h1:maD7wRr/U5Z6m/iR4s+kqSMx2CaBsrgA7czyZG/E6dU=
-github.com/creack/pty v1.1.7 h1:6pwm8kMQKCmgUg0ZHTm5+/YvRK0s3THD/28+T6/kk4A=
 github.com/creack/pty v1.1.7/go.mod h1:lj5s0c3V2DBrqTV7llrYr5NG6My20zk30Fl46Y7DoTY=
+github.com/creack/pty v1.1.15 h1:cKRCLMj3Ddm54bKSpemfQ8AtYFBhAI2MPmdys22fBdc=
+github.com/creack/pty v1.1.15/go.mod h1:MOBLtS5ELjhRRrroQr9kyvTxUAFNvYEK993ew/Vr4O4=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -337,7 +338,6 @@ github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFB
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/pty v1.1.8 h1:AkaSdXYQOWeaO3neb8EM634ahkXXe3jYbVh/F9lq+GI=
 github.com/kr/pty v1.1.8/go.mod h1:O1sed60cT9XZ5uDucP5qwvh+TE3NnUj51EiZO/lmSfw=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=