(MCO-816) Allow upgrading puppet-agent with mcollective

Since mcollective is part of puppet-agent packaging, upgrading that
package over an mcollective plugin is tricky. Previously the mcollective
systemd service was currently configured in a way that broke that,
because it killed the entire process tree when stopping as part of the
upgrade.

Set `KillMode=process` for the systemd service (similar to how Puppet
and PXP Agent are configured) so that it can be restarted during the
upgrade without killing the upgrade itself.

ext/aio/redhat/mcollective.service

@@ -19,6 +19,7 @@ StandardError=syslog
ExecStart=/opt/puppetlabs/puppet/bin/mcollectived --config=/etc/puppetlabs/mcollective/server.cfg --pidfile=/var/run/puppetlabs/mcollective.pid --daemonize
ExecReload=/bin/kill -USR1 $MAINPID
PIDFile=/var/run/puppetlabs/mcollective.pid
KillMode=process

[Install]
WantedBy=multi-user.target

ext/redhat/mcollective.service

@@ -19,6 +19,7 @@ StandardError=syslog
ExecStart=/usr/sbin/mcollectived --config=/etc/mcollective/server.cfg --pidfile=/var/run/mcollective.pid --no-daemonize
ExecReload=/bin/kill -USR1 $MAINPID
PIDFile=/var/run/mcollective.pid
KillMode=process

[Install]
WantedBy=multi-user.target