Per review comments in https://gerrit.hyperledger.org/r/#/c/15057/

 ,
the index warming in the commit path will impact performance, it needs
to be moved out of commit path in a separate goroutine or daemon.

This change executes the WarmIndexAllIndexes() as a background process.

Change-Id: I706cae02d1e07551849ae301381f2b3ff218ade8
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>