Motivation:

 - performance benchmarking
 - getting in touch with JMH

Modification:
Add throughput test for lock manager. Introduce a dedicated profile to
run benchmark tests.

```
$ mvn clean verify -Pbenchmark

....

Result "org.dcache.nfs.benchmarks.ConcurrentLockManagerBenchmark.benchmarkConcurrentLocking":
  1574556.068 ±(99.9%) 98632.233 ops/s [Average]
  (min, avg, max) = (1078256.296, 1574556.068, 1735655.142), stdev = 131671.209
  CI (99.9%): [1475923.835, 1673188.301] (assumes normal distribution)

$
```

Result:
automated performance monitoring can be integrated into CI.

Acked-by: Albert Rossi
Target: master