HBASE-10567 Add overwrite manifest option to ExportSnapshot

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1570502 13f79535-47bb-0310-9956-ffa450edef68
HBASE-10516 Refactor code where Threads.sleep is called within a while/for loop (Feng Honghua)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1570524 13f79535-47bb-0310-9956-ffa450edef68