Increase container shutdown delay before force-killing to avoid db
corruption after controller reboots
Parameterize SHUTDOWNDELAY envvar as lxc_container_shutdown_delay
with default value 60 seconds
Rename lxc.default.j2 template to lxc-net.default.j2 to align with
destination config file name lxc-net
Add new lxc.default.j2 template to use the lxc_container_shutdown_delay
variable and allow user-defined value
Related-Bug: 1806696
Change-Id: I1d3b7990e462140fdb402883f8d25422eafca66b
d0d9384aee