Apply dynamic scheduling to cc_sv hooking loop

[hcoffey1]

This PR adjusts the OpenMP scheduler for the hooking loop in cc_sv.

The current scheduler performs a static partitioning of the loop iterations, but for structured graphs like twitter.sg where connections are concentrated in certain node index ranges, this leads to thread workload imbalance.

If we use 4 worker threads on the twitter graph and examine how the current static partitioning works, we see threads 0, 2, and 3 are assigned less intensive portions of the graph.

Below is a bandwidth-estimate measurement with a tool I worked on, ZRay. The run is performing 5 trials. Threads 0, 2, and 3 are largely idle.

Updating the OpenMP pragma to match the scheduler currently used in cc, the thread imbalance is resolved.
#pragma omp parallel for schedule(dynamic, 16384)

This leads to about a 2.5X speedup when processing the twitter.sg graph.

Before:

/mydata/gapbs (cc_sv-dynamic-schedule) » OMP_NUM_THREADS=4 numactl --m 0 -N 0 ./cc_sv -f ./benchmark/graphs/twitter.sg -n 5
Read Time:           47.86347
Graph has 61578171 nodes and 1053505858 directed edges for degree: 17
Shiloach-Vishkin took 4 iterations
Trial Time:          29.98726
Shiloach-Vishkin took 4 iterations
Trial Time:          29.99018
Shiloach-Vishkin took 4 iterations
Trial Time:          29.99191
Shiloach-Vishkin took 4 iterations
Trial Time:          29.98698
Shiloach-Vishkin took 4 iterations
Trial Time:          29.98203
Average Time:        29.98767

After:

/mydata/gapbs (cc_sv-dynamic-schedule*) » OMP_NUM_THREADS=4 numactl --m 0 -N 0 ./cc_sv -f ./benchmark/graphs/twitter.sg -n 5
Read Time:           47.89368
Graph has 61578171 nodes and 1053505858 directed edges for degree: 17
Shiloach-Vishkin took 4 iterations
Trial Time:          11.70602
Shiloach-Vishkin took 4 iterations
Trial Time:          11.32988
Shiloach-Vishkin took 3 iterations
Trial Time:          8.99948
Shiloach-Vishkin took 4 iterations
Trial Time:          11.71223
Shiloach-Vishkin took 4 iterations
Trial Time:          11.71172
Average Time:        11.09187