agl-lxc: Stably start lxc service after drm-lease-manager

agl-lxc: Stably start lxc service after drm-lease-manager

Since there is some race condition between initialization of
drm-lease-manager and startup of lxc guest images in
lxc-host-image-demo currently, we sometimes observe a startup
failure of the cluster-guest, especially on refhw platform,
due to delay of lease device creation.

This change adds unit dependencies between lxc and
drm-lease-manager so that lxc guests can be started after lease
devices creation stably.

Bug-AGL: SPEC-4427

Signed-off-by: Hiroyuki Ishii <ishii.hiroyuki002@jp.panasonic.com>
Change-Id: I16183c784d8e1132ba316f842e5dedc664ec2853