Metrics id resolver should be able to resolve metrics in bulk.

[octo47]

We are migrating our old system and due of its architecture we have a substantial rate of metrics variations. After daemon started cache filled with gets to 'tsdb-uid' table with followed join() on Deferred. This leads to syncronous requests to hbase. In case of our rate (tens of thousands) we doing slow cache filling.
Cache in opentsdb should be able to resolve ids in a bulk.

All OpenTSDBSink threads looks like:

Thread 12136: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.Object.wait() @bci=2, line=485 (Interpreted frame)
 - com.stumbleupon.async.Deferred.doJoin(boolean, long) @bci=77, line=1122 (Interpreted frame)
 - com.stumbleupon.async.Deferred.joinUninterruptibly() @bci=3, line=1048 (Interpreted frame)
 - net.opentsdb.uid.UniqueId.hbaseGet(byte[], byte[], org.hbase.async.RowLock) @bci=48, line=585 (Interpreted frame)
 - net.opentsdb.uid.UniqueId.hbaseGet(byte[], byte[]) @bci=4, line=573 (Interpreted frame)
 - net.opentsdb.uid.UniqueId.getIdFromHBase(java.lang.String) @bci=8, line=209 (Interpreted frame)
 - net.opentsdb.uid.UniqueId.getId(java.lang.String) @bci=35, line=189 (Interpreted frame)
 - net.opentsdb.uid.UniqueId.getOrCreateId(java.lang.String) @bci=15, line=234 (Interpreted frame)
 - net.opentsdb.core.IncomingDataPoints.rowKeyTemplate(net.opentsdb.core.TSDB, java.lang.String, java.util.Map) @bci=76, line=124 (Interpreted frame)
 - net.opentsdb.core.IncomingDataPoints.setSeries(java.lang.String, java.util.Map) @bci=12, line=139 (Interpreted frame)
 - ru.yandex.opentsdb.flume.OpenTSDBSink$State.writeDataPoints(java.util.List) @bci=42, line=103 (Interpreted frame)
 - ru.yandex.opentsdb.flume.OpenTSDBSink$State.access$700(ru.yandex.opentsdb.flume.OpenTSDBSink$State, java.util.List) @bci=2, line=73 (Interpreted frame)
 - ru.yandex.opentsdb.flume.OpenTSDBSink$1.call() @bci=238, line=368 (Interpreted frame)
 - ru.yandex.opentsdb.flume.OpenTSDBSink$1.call() @bci=1, line=332 (Interpreted frame)
 - java.util.concurrent.FutureTask$Sync.innerRun() @bci=30, line=303 (Interpreted frame)
 - java.util.concurrent.FutureTask.run() @bci=4, line=138 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor$Worker.runTask(java.lang.Runnable) @bci=59, line=886 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=28, line=908 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=662 (Interpreted frame)