ensure that placement with https uses the -s flag when checking health

On a cloud when placement gets ssl certs added, we see that the placement checks fail because `-S` isn't added.

As an example:

root@<redacted>:/etc/nagios/nrpe.d# cat check_placement_admin.cfg
# check placement_admin
# The following header was added automatically by juju
# Modifying it will affect nagios monitoring and alerting
# servicegroups: juju
command[check_placement_admin]=/usr/lib/nagios/plugins/check_http -H placement-internal.openstack-<redacted>.com -p 8778 -u /healthcheck -e Unauthorized -d x-openstack-request-id
root@<redacted>:/etc/nagios/nrpe.d# /usr/lib/nagios/plugins/check_http -H placement-internal.openstack-<redacted>.com -p 8778 -u /healthcheck -e Unauthorized -d x-openstack-request-id
HTTP CRITICAL - Invalid HTTP response received from host on port 8778: HTTP/1.1 400 Bad Request

compared to when we add the -S flag:

root@<redacted>:/etc/nagios/nrpe.d# /usr/lib/nagios/plugins/check_http -H placement-internal.openstack-<redacted>.com -p 8778 -u /healthcheck -e Unauthorized -d x-openstack-request-id -S
HTTP OK: Status line output matched "Unauthorized" - 429 bytes in 0.008 second response time |time=0.008035s;;;0.000000;10.000000 size=429B;;;0