~hloeung/ubuntu-repository-cache/no-apache2-mpm-MaxConnectionsPerChild

Handle when newly provisioned unit

Newly provisioned units set the charm's failover feature. This sets up proxying of all requests to the last u-r-c unit. This means that the health-check will succeed as it's checking on the previous unit.

We want to fix this by not proxying the health-check endpoint URL (/_health-check/health-check.py). We also want to set the health-check's 'disabled for maintenance' flag when the charm's failover feature is activated.

Finally, update the health-check to ensure ubuntu_active is present. It's not present on initial metadata sync.

Reviewed-on: https://code.launchpad.net/~hloeung/ubuntu-repository-cache/health-check-handle-initial-sync/+merge/398100
Reviewed-by: Nick Moffitt <nick.moffitt@canonical.com>
Reviewed-by: Tom Haddon <tom.haddon@canonical.com>
Reviewed-by: Laurent Sesques <laurent.sesques@canonical.com>