Dead child does not get reapped, relaunched

Description of Issue

When the grandchild of the main salt-minion process dies for some reason, its parent does not reap it, leaving it zombie, and not relaunching it. Also, the minion stops responding to ping.

Steps to Reproduce Issue

# ps faux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
[...]
root      8481  0.0  0.2 314152 22124 ?        Ss   11:43   0:00 /usr/bin/python /usr/bin/salt-minion
root      8487  0.1  0.5 630420 44692 ?        Sl   11:43   0:11  \_ /usr/bin/python /usr/bin/salt-minion
root      8491  0.0  0.2 404020 20824 ?        S    11:43   0:00      \_ /usr/bin/python /usr/bin/salt-minion

Picked the last one, killed it:

# kill 8491
# ps faux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
[...]
root      8481  0.0  0.2 314152 22124 ?        Ss   11:43   0:00 /usr/bin/python /usr/bin/salt-minion
root      8487  0.1  0.5 630420 44692 ?        Sl   11:43   0:12  \_ /usr/bin/python /usr/bin/salt-minion
root      8491  0.0  0.0      0     0 ?        Z    11:43   0:00      \_ [salt-minion] <defunct>

Versions Report (all nodes)

Salt Version:
           Salt: 2019.2.0
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.7.2
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 2.7.5 (default, Aug  4 2017, 00:39:18)
   python-gnupg: Not Installed
         PyYAML: 3.10
          PyZMQ: 14.3.1
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 3.2.5
 
System Versions:
           dist: centos 7.4.1708 Core
         locale: UTF-8
        machine: x86_64
        release: 3.10.0-693.el7.x86_64
         system: Linux
        version: CentOS Linux 7.4.1708 Core

Start at the salt-minion entry point and reproduce the process hierarchy described in the issue on Linux. Trace how the grandchild is supervised after termination; done means the child is reaped, a replacement is launched, and the minion responds to ping again.