Redesign Host storage to use an actual HarddriveStorage
instead of just a Storage (which is now called SimpleStorage).
This way, we can define disk parameters such as reading speed
that is considered when virtual memory is required
by Cloudlets running inside a VM on the Host.

The FileStorage interface implemented by HarddriveStorage
is now simpler, since we don't want to simulate individual file storage
for hard drive, only for SanStorage.

Adds new Host constructor to accept a HarddriveStorage instead of a long
for defining the storage device.

Since VM and Host have different storage devices now
(SimpleStorage and HarddriveStorage, respectively),
the AbstractMachine interface now is generic,
to indicate the kind of storage to be used by
subclasses.

Signed-off-by: Manoel Campos <[email protected]>

…wap) delay

- Introduces cloudlet processing delay when a cloudlet
  requires more RAM than there is freely available.
- As a simplification, there is no pre-defined swap partition to define
  the maximum amount of virtual memory to use.
  The virtual memory required just needs to be smaller than the
  RAM capacity.
- Updates used VM resources for each processed cloudlet,
  instead of iterating over the cloudlets execution list
  at the end of the updateProcessing method.
  This improves simulation performance and accuracy,
  since for each processed cloudlet, VM resource utilization
  is updated right-away.
- Since using VMem requires some portion of the RAM to be swapped between the disk
  to open up RAM space, the required RAM cannot be higher then the RAM capacity
  neither than the available disk space.
- Adds important notes about the simplified implementation of Virtual Memory (VMem / memory swapping)

Signed-off-by: Manoel Campos <[email protected]>

Signed-off-by: Manoel Campos <[email protected]>