Don't remove data before rerunning chef cookbooks

All our cookbooks now support in-place updates.
Add Decision Engine tutorial to the sandbox
Switch from dt-data to phantom-cookbooks tarballs
Catch socket errors when importing a key

This includes "[Errno 111] Connection refused" when a cloud is down
(e.g. for maintenance).
Merge branch 'master' into phantom0.2

Conflicts:
	plan/common/deps.conf
Update global variables for cookbooks URL