Backport HBASE-9426(Make custom distributed barrier procedure pluggable) to 0.98.x

Backport HBASE-9426 to better leverage snopshot feature on 0.98.x.

We(IBM) are in process to open source our solution of Backup/Restore through HBASE-7912. The solution is using distributed log roll or distributed table flush and depending on the feature provided by HBase-9426