Add admin end point for metrics

Adds following 

* all the jvm metrics to be exposed as part of server metrics
* Adds host:port/admin with end points for ping, metrics, threads and healthcheck. Healthcheck is not implemented yet
Ex:
>http://localhost:9999/admin/ping
<pong
>http://localhost:9999/admin/threads
< {all jvm thread information}
>http://localhost:9999/admin/metrics
<
{
  "version" : "3.0.0",
  "gauges" : {
    "gc.ConcurrentMarkSweep.count" : {
      "value" : 0
    },
    "gc.ConcurrentMarkSweep.time" : {
      "value" : 0
    },
    "gc.ParNew.count" : {
      "value" : 21
    },
    "gc.ParNew.time" : {
      "value" : 152
    },
    "jvm.name" : {
      "value" : "pid@<hostname>"
    },
    "jvm.uptime" : {
      "value" : 48816
    },
    "jvm.vendor" : {
      "value" : "Apple Inc. Java HotSpot(TM) 64-Bit Server VM 20.65-b04-462 (1.0)"
    },
    "memory.heap.committed" : {
      "value" : 85000192
    },
    "memory.heap.init" : {
      "value" : 0
    },
    "memory.heap.max" : {
      "value" : 1065025536
    },
    "memory.heap.usage" : {
      "value" : 0.023105556785447817
    },
    "memory.heap.used" : {
      "value" : 24608008
    },
    "memory.non-heap.committed" : {
      "value" : 59183104
    },
    "memory.non-heap.init" : {
      "value" : 24317952
    },
    "memory.non-heap.max" : {
      "value" : 136314880
    },
    "memory.non-heap.usage" : {
      "value" : 0.4321687551645132
    },
    "memory.non-heap.used" : {
      "value" : 58911032
    },
    "memory.pools.CMS-Old-Gen.usage" : {
      "value" : 0.017588715834260613
    },
    "memory.pools.CMS-Perm-Gen.usage" : {
      "value" : 0.6516127237459508
    },
    "memory.pools.Code-Cache.usage" : {
      "value" : 0.057285308837890625
    },
    "memory.pools.Par-Eden-Space.usage" : {
      "value" : 0.09140556227992958
    },
    "memory.pools.Par-Survivor-Space.usage" : {
      "value" : 0.10059052660949248
    },
    "memory.total.committed" : {
      "value" : 144183296
    },
    "memory.total.init" : {
      "value" : 24317952
    },
    "memory.total.max" : {
      "value" : 1201340416
    },
    "memory.total.used" : {
      "value" : 83519040
    },
    "threads.blocked.count" : {
      "value" : 0
    },
    "threads.count" : {
      "value" : 35
    },
    "threads.daemon.count" : {
      "value" : 29
    },
    "threads.deadlocks" : {
      "value" : [ ]
    },
    "threads.new.count" : {
      "value" : 0
    },
    "threads.runnable.count" : {
      "value" : 9
    },
    "threads.terminated.count" : {
      "value" : 0
    },
    "threads.timed_waiting.count" : {
      "value" : 8
    },
    "threads.waiting.count" : {
      "value" : 18
    }
  },
  "counters" : {
    "com.inmobi.grill.server.GrillRequestListener.http-requests-finished" : {
      "count" : 1
    },
    "com.inmobi.grill.server.GrillRequestListener.http-requests-started" : {
      "count" : 1
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.finished-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.queued-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.running-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.total-cancelled-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.total-failed-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.total-finished-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.total-queued-queries" : {
      "count" : 0
    },
    "com.inmobi.grill.server.api.query.QueryExecutionService.total-success-queries" : {
      "count" : 0
    }
  },
  "histograms" : { },
  "meters" : { },
  "timers" : { }
}