qisrc reset --snapshot: several bug fixes

* Actually configure the manifest when given a json snaphshot
* Fail when configuring manifest fails

Change-Id: I63f44a03c9aa5d332bffaff7918984907789cf17
Reviewed-on: http://gerrit.aldebaran.lan/41437
Reviewed-by: vbarbaresi <vbarbaresi@aldebaran-robotics.com>
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Tested-by: gerrit
Tested-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>