Upgrade to Docker remote API v1.8

Signed-off-by: Maxime Petazzoni <max@signalfuse.com>
Support and expand environment variables defined as YAML lists

Signed-off-by: Maxime Petazzoni <max@signalfuse.com>
Fail faster on container ping if the container goes down

Signed-off-by: Maxime Petazzoni <max@signalfuse.com>