When configuring Docker we need to kill persistent SSH connections to
refresh the membership of the docker group for the stack user. Currently
we are using a fairly heavy handed method of removing all ControlPersist
sockets because the Ansible reset_connection meta module previously did
not work [1]. This issue is fixed since Ansible 2.5.6.
This change switches to the reset_connection meta module, which now
works as expected.
[1] https://github.com/ansible/ansible/issues/27520
Change-Id: Id4d951e447720e1d769491c0d34ad83099c030eb
6ca967e27f