Retry on listkeys timeout

loaded upgrade has a tendency to fail on listkeys time out, which should
not make the fail test. Made the PB client have the auto_reconnect flag
set and added functions to retry reconnecting (as it doesn't happen
instantaneously) and retry the list keys a few times with exponentially
bigger time outs.
Link PB client to check listkeys process

As pointed out by Sean Cribbs, it's kind of weird to have it linked to
the main process like it is now.
Merge pull request #162 from basho/eas-retry-on-listkeys-timeout

Fix loaded_upgrade list key time outs