Prepare for Maestro 0.1.7

Signed-off-by: Maxime Petazzoni <max@signalfuse.com>
Upgrade to Maestro 0.1.7.1 and pin to Docker 0.8

Even though Docker 0.10 is out and 0.11 is around the corner, for now
our compatibility is verified and validated with 0.8 only, so let's pin
us to that for now until Maestro and docker-py are fully validated with
Docker >= 0.10.

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