Store 'clone' timestamps in Redis database

Using redis keys to store clone timestamps will allow for a global TTL
for VMs in the 'pending' pool; failed clones should be cleaned up and
retried after a set period of time (eg. 15m).
Adding missing 'start' variable
Merge pull request #3 from sschneid/clone_timestamp_in_redis

Store VM 'clone' timestamp in Redis