HDFS-4826. TestNestedSnapshots times out due to repeated slow edit log flushes when running on virtualized disk.  Contributed by Chris Nauroth


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1483150 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4311-trunk-gd