usermod/userdel errantly believe user has running processes

I have found an occasional inability to remove or modify users due to incorrect matching of process owners, e.g.

# id -u bdobbs
1047
# usermod -u 1573552 bdobbs
usermod: user bdobbs is currently used by process 6337
# cat /proc/6337/status | grep Uid
Uid: 3000400 3000400 3000400 3000400

In `libmisc/user_busy.c` a check is performed for processes owned by a user which is being modified. Searching subordinate user IDs causes errant matches. This has been fixed upstream, and is included in passwd-4.8 and the issue does not appear to exist in groovy.

https://github.com/shadow-maint/shadow/commit/fd4405b763d26649339069532e79bd45013c8c38 I believe this fix should be backported to xenial and bionic.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: passwd 1:4.2-3.1ubuntu5.4
ProcVersionSignature: Ubuntu 4.4.0-1107.118-aws 4.4.219
Uname: Linux 4.4.0-1107-aws x86_64
ApportVersion: 2.20.1-0ubuntu2.23
Architecture: amd64
Date: Tue May 26 22:18:00 2020
Ec2AMI: ami-4e79ed36
Ec2AMIManifest: (unknown)
Ec2AvailabilityZone: us-west-2a
Ec2InstanceType: t3.medium
Ec2Kernel: unavailable
Ec2Ramdisk: unavailable
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/zsh
SourcePackage: shadow
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.cron.daily.passwd: [deleted]