Added unit tests to test code in def/ module.
Currently, AverageNodePowerHistory(...) assumes that the DRAM power
readings are being monitored. In addition, it also assumes that the
host servers are dual socket machines. However, this assumption might
not always hold true. Thus, added a TODO to fix this.
Degree of collocation logger (or task share variance logger) was
only present in pcp.go. Copied that code into extrema and prog-extrema.
Also, exposed visibility of pcp/utils.go#cpuUtilsPerNode(...) and
pcp/utils.go#memUtilsPerNode(...) to public.
