Increase delay and retries for lxc cache download

This may increase run time, but thats better than having to re-run, esp
in the gate.

Related: #449
(cherry picked from commit 90f2b82c92789dcdf00fad51f657f5bb5cf4a4fd)
Merge pull request #469 from claco/stable/icehouse

backport - stable/icehouse - Increase delay and retries for lxc cache download