lxd/instance: Reworks autoCreateInstanceSnapshots and autoCreateInstanceSnapshotsTask to use InstancesToInstanceArgs
lxd/instance: Reworks autoCreateInstanceSnapshots and autoCreateInstanceSnapshotsTask to use InstancesToInstanceArgs

This avoids the minutely CPU bursts due to inefficient queries when there are lots of instances.

Also cleans up comments and naming to indicate these functions operate on instances,
not just containers.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

lxc/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd