[OMID-39] Implement coprocessor metrics in Hadoop

[francisco-perez-sorrosal]

Discuss with the community if this is the right thing to do when adding metrics to a coprocessor.

Histograms added: -time on compactions -time on processing a cell -time on contacting commit table for retrieve a commit TS (RPC)

Counters added: -major & minor compactions -scanned rows (in all compactions) -total cells explored (in all compactions) -retained cells (in all compactions) -shadow cells healed (in all compactions) -discarded cells (in all compactions) -tombstone cells found (in all compactions)

Change-Id: I4a3607f1992505896e674ddb073a51ebf2582550