This CR allows building of block storage indexes.
For rebuilding the indexes, existing index folder would need to be dropped.
However, please note that this would drop (and rebuild) the indexes for all
the chains because they share the underlying leveldb.

Also, enabled the flush/synch of batch writting to leveldb (statedb, block indexes, and historydb).

Change-Id: I6a926ab765df4bbb6543d6a3960359d95d60fd68
Signed-off-by: manish <manish.sethi@gmail.com>