Added a new field "terminate" to tracefile

This new field, if present, indicates when the machine is terminated by
the user.
Improve the termination of instances and jobs

Now it is possible to specify after how many seconds the instances will
be terminated.
First attemp to write output files
Remove some output until we handle it
Take into account CoW images
remove print statements and use Python logging instead
Move cloud.Job object into its own module
Use "import nova.exception"
Move cloud.Instance object into its own module
Move cloud.Request object into its own module
Moved cloud.Host object into its own module
Code cleanup