Implement first version of job execution

This not so nice patch adds submit/wait-for-completion functionality in
hbal. When enabled via ‘-X’ (only working on Luxi), it executes the jobs
(as split into separate jobsets by Cluster.splitJobs) and waits until
ganeti has finished all of them.

This is a rough version: it waits ad infinitum for completion, has
hardcoded timeouts, etc.

Signed-off-by: Iustin Pop <iustin@google.com>