HBASE-10599 Replace System.currentMillis() with EnvironmentEdge.currentTimeMillis in memstore flusher and related places (Ramkrishna S. Vasudevan)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1577702 13f79535-47bb-0310-9956-ffa450edef68