Add a service enable/disable mechanism for upstart

Upstart doesn't have its own service enable/disable mechanism. We are in
need of a facility to enable/disable services without writing to /etc at
runtime to enable a readonly root for image based updates. This command
will be used by later changes to have a generic service enable/disable
mechanism for all init systems.

Change-Id: I931281988aa746f93de190794f68f4c9e628db19
Enable services with os-svc-enable

Split out the code which enables services to start on boot into
a new os-svc-enable script. This script is currently called by
os-svc-deamon so that services automatically start on first boot
(as is the case with os-svc-install)

The motivation here is to decouple service installation and enabling
so that we can eventually avoid starting services on first boot
until after they are configured. Auto starting services on boot like
we currently do is causing lots of log ERROR messages, etc.

Change-Id: I66d4660c169f5918e924eab1876134891c3a24a1
Merge "Add a service enable/disable mechanism for upstart"
Merge "Enable services with os-svc-enable"