Housekeeping: small TODOs and minor improvements #591

Small, independent TODOs. Each one can be fixed in its own commit.

Possible bugs

• utilizationmodels/UtilizationModelPlanetLab.java: the interval size should add 1, but it uses the original formula.
  Check the impact on tests (fixing it may change simulation results).
• selectionpolicies/VmSelectionPolicyMinimumMigrationTime.java: the migration time is computed from the RAM capacity.
  It must use the current RAM usage and also consider the VM size (see DatacenterSimple.timeToMigrateVm).

Redundant or unused API

• core/SimEntity.java: isStarted and isAlive seem to be redundant.
• cloudlets/Cloudlet.java: an attribute that seems unused and should be removed (confirm first).
• vms/Vm.java: isSuitableForCloudlet isn't called anywhere.
• vms/VmAbstract.java: a method that is confusing because there is also a getRequestedMips() (generated by Lombok).

Design

• faultinjection/HostFaultInjection.java: the class has multiple responsibilities.
  Fault injection must be separated from fault recovery (the cloner methods). Also fix the 2TODO typo.
• resources/SanStorage.java: see the warning in the class documentation.
• distributions/PoissonDistr.java: the PoissonDistribution from Apache Commons Statistics is only used to compute
  eventsArrivalProbability(). It could also generate the random numbers, like the classes extending ContinuousDistributionAbstract.
• distributions/PoissonDistr.java: a method that should be moved to an example class that creates Cloudlets.

Performance

• heuristics/Heuristic.java: try to parallelize the solution search (e.g. using parallel streams).