ftests: Init LXC in a separate thread

ftests: Init LXC in a separate thread

Occasionally LXC fails with a socket timeout error when running
on Github Actions.  To alleviate this, run `lxc init` in a separate
thread.  While init is running, periodically print an inane log
message in an attempt to appease Github Actions.  If `lxc init`
fails, Container() will now retry the init up to five times.

	Error: Failed instance creation: write unix
	@->/var/snap/lxd/common/lxd/unix.socket: i/o timeout

	Error: Failed instance creation: websocket: close 1006
	(abnormal closure): unexpected EOF

Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
Reviewed-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>