agent: recover from 437 error with new sockets

When a 437 error is received for an allocate request, it
means that the TURN server already has a matching allocation for the
5-tuple.  This can happen rarely when lots of clients are behind the
same NAT using the same TURN server.  The recovery is to try
again with a different 5-tuple (i.e. use a new socket).
11 jobs for master in 6 minutes and 43 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #2683129
build autotools

00:00:58

passed #2683130
build meson

00:00:26

passed #2683132
1809 windows docker
build msvc amd64

00:05:10

passed #2683133
1809 windows docker
build msvc x86

00:05:14

failed #2683131
1809 windows docker allowed to fail
build msys2

00:06:43

 
  Test
passed #2683136
distcheck autotools

00:02:09

passed #2683139
doc-and-install meson

00:00:41

passed #2683134
test autotools

00:04:24

passed #2683135
test autotools valgrind

00:04:42

passed #2683137
test meson

00:01:06

passed #2683138
test valgrind meson

00:01:08

 
Name Stage Failure
failed
build msys2 Build
GO version:   go1.13.8
Built: 2020-04-21T11:59:25+0000
OS/Arch: windows/amd64
Uploading artifacts...
build/meson-logs/: found 2 matching files

build/build.ninja: found 1 matching files

WARNING: Failed to load system CertPool: crypto/x509: system root pool is not available on Windows
Uploading artifacts to coordinator... ok
id=2683131 responseStatus=201 Created token=NWtE9sQt
ERROR: Job failed: exit code 1