Returns {@link SchedulingPolicy} instance corresponding to the
   * {@link SchedulingPolicy} passed as a string. The policy can be "fair" for
   * FairSharePolicy, "fifo" for FifoPolicy, or "drf" for
   * DominantResourceFairnessPolicy. For a custom
   * {@link SchedulingPolicy}s in the RM classpath, the policy should be
   * canonical class name of the {@link SchedulingPolicy}.
Returns {@link SchedulingPolicy} instance corresponding to the
   * {@link SchedulingPolicy} passed as a string. The policy can be "fair" for
   * FairSharePolicy, "fifo" for FifoPolicy, or "drf" for
   * DominantResourceFairnessPolicy. For a custom
   * {@link SchedulingPolicy}s in the RM classpath, the policy should be
   * canonical class name of the {@link SchedulingPolicy}. | SchedulingPolicy.java