Add lock to filesCompacting in all place.

We find regionserver abort with the following exception:

2017-05-09 17:40:06,369 FATAL [regionserver/hadoop0349.et2.tbsite.net/11.251.152.199:16020-shortCompactions-1493026663275] regionserver.HRegionServer: ABORTING region server hadoop0349.et2.tbsite.net,16020,1493026637177: Thread[regionserver/hadoop0349.et2.tbsite.net/11.251.152.199:16020-shortCompactions-1493026663275,5,main] throw uncaught exception
java.lang.ArrayIndexOutOfBoundsException
        at java.lang.System.arraycopy(Native Method)
        at java.util.ArrayList.batchRemove(ArrayList.java:726)
        at java.util.ArrayList.removeAll(ArrayList.java:690)
        at org.apache.hadoop.hbase.regionserver.HStore.finishCompactionRequest(HStore.java:1666)
        at org.apache.hadoop.hbase.regionserver.HStore.cancelRequestedCompaction(HStore.java:1656)
        at org.apache.hadoop.hbase.regionserver.CompactSplitThread$CompactionRunner.run(CompactSplitThread.java:504)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1147)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
        at java.lang.Thread.run(Thread.java:834)

2017-05-08 21:15:31,979 FATAL [regionserver/hadoop1191.et2.tbsite.net/11.251.159.40:16020-longCompactions-1494249331978] regionserver.HRegionServer: ABORTING region server hadoop1191.et2.tbsite.net,16020,1493196567798: Thread[regionserver/hadoop1191.et2.tbsite.net/11.251.159.40:16020-longCompactions-1494249331978,5,main] throw uncaught exception
java.lang.IllegalArgumentException
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:76)
        at org.apache.hadoop.hbase.regionserver.compactions.RatioBasedCompactionPolicy.getCurrentEligibleFiles(RatioBasedCompactionPolicy.java:64)
        at org.apache.hadoop.hbase.regionserver.compactions.RatioBasedCompactionPolicy.preSelectCompactionForCoprocessor(RatioBasedCompactionPolicy.java:72)
        at org.apache.hadoop.hbase.regionserver.DefaultStoreEngine$DefaultCompactionContext.preSelect(DefaultStoreEngine.java:117)
        at org.apache.hadoop.hbase.regionserver.HStore.requestCompaction(HStore.java:1542)
        at org.apache.hadoop.hbase.regionserver.CompactSplitThread.selectCompaction(CompactSplitThread.java:362)
        at org.apache.hadoop.hbase.regionserver.CompactSplitThread.access$200(CompactSplitThread.java:58)
        at org.apache.hadoop.hbase.regionserver.CompactSplitThread$CompactionRunner.run(CompactSplitThread.java:491)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1147)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
        at java.lang.Thread.run(Thread.java:834)

HStore#finishCompactionRequest do not require any HStore#lock's lock so HStore.replaceStoreFiles need to synchronized on filesCompacting.